It's working again! Hooray!! I have no good explanation for why the following changes worked; it's a puzzle of it's own. But here's what I did:
Out of frustration and almost-random trial and error, I changed my router settings and the IP V4 configuration of the adapter in the problematic computer. I changed the fixed IP address from 192.168.1.106 to 192.168.1.112, but I also changed the DNS settings from 75.75.75.75/75.75.76.76 to using the router's IP as the first DNS address, as follows: 192.168.1.100/75.75.75.75
And after that, I connected to the Internet just fine!
That doesn't make any sense at all to me (but neither did I understand why it wasn't working as it was, of course). I double-checked and triple-checked to ensure that there was no other device trying to use 192.168.1.106. I confirmed this not only in the router's settings, but also using a tool called
Advanced IP Scanner.
That being the case, I can't help thinking that changing the DNS address is what fixed the problem, but
that doesn't make any sense either! All my other Ethernet connected XP Pro machines have their DNS settings set to 75.75.75.75/75.75.76.76, and they connect to the Internet without problems. The only thing I can think of that is at all different is that the BADXP machine's Ethernet was connected via a power-line adapter (as are three other non-computers which always connected fine). Besides, the problem almost certainly wasn't related to DNS issues since I also couldn't ping to known IP addresses from the web (such as 74.125.225.100 for Google.com).
But there was one more puzzling oddity. Earlier, before I tried uninstalling all the most recent Windows Updates to get it working, I cloned a copy of the system partition that included all the updates already. After the IP changes described in this post, and being able to connect to the Internet again, perhaps foolishly I decided to restore that cloned copy back to the boot system partition. After it booted up, I made the same changes (IP = 192.168.1.112, DNS = 192.168.1.100/75.75.75.75), and rebooted. However, this time it wouldn't connect again!
Frustrated and angry at myself, I played around with the usual set of trial-and-error changes to the XP Network settings, such as disabling and re-enabling the NIC, performing a "repair" (flush DNS cache, etc), and the like. Eventually, it connected to the Internet again! So I immediately created a new restore point, backed up my settings, and created a new cloned backup of the now-working system partition.
Finally, everything is working perfectly again!
Here's the latest report of my working IP and related settings:
MiniToolBox by Farbar Version: 23-01-2014
Ran by xxx (administrator) on 22-03-2014 at 00:34:06
Running from "C:\Documents and Settings\xxx\Desktop"
Microsoft Windows XP Professional Service Pack 3 (X86)
Boot Mode: Normal
***************************************************************************
========================= Hosts content: =================================
127.0.0.1 localhost
========================= IP Configuration: ================================
Intel® 82567LF-2 Gigabit Network Connection = Local Area Connection (Connected)
The following command was not found: int ip dump.
Windows IP Configuration
Host Name . . . . . . . . . . . . : shoebox
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel® 82567LF-2 Gigabit Network Connection
Physical Address. . . . . . . . . : 00-1C-C0-6F-B7-48
Dhcp Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 192.168.1.112
Subnet Mask . . . . . . . . . . . : 255.255.255.0
IP Address. . . . . . . . . . . . : fe80::21c:c0ff:fe6f:b748%4
Default Gateway . . . . . . . . . : 192.168.1.100
DNS Servers . . . . . . . . . . . : 192.168.1.100
75.75.75.75
fec0:0:0:ffff::1%1
fec0:0:0:ffff::2%1
fec0:0:0:ffff::3%1
Tunnel adapter Teredo Tunneling Pseudo-Interface:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : FF-FF-FF-FF-FF-FF-FF-FF
Dhcp Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : fe80::ffff:ffff:fffd%5
Default Gateway . . . . . . . . . :
NetBIOS over Tcpip. . . . . . . . : Disabled
Tunnel adapter Automatic Tunneling Pseudo-Interface:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Automatic Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : C0-A8-01-70
Dhcp Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : fe80::5efe:192.168.1.112%2
Default Gateway . . . . . . . . . :
DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1
fec0:0:0:ffff::2%1
fec0:0:0:ffff::3%1
NetBIOS over Tcpip. . . . . . . . : Disabled
Server: cdns01.comcast.net
Address: 75.75.75.75
Name: google.com
Addresses: 74.125.225.101, 74.125.225.99, 74.125.225.96, 74.125.225.103
74.125.225.110, 74.125.225.102, 74.125.225.104, 74.125.225.97, 74.125.225.98
74.125.225.100, 74.125.225.105
Pinging google.com [74.125.225.71] with 32 bytes of data:
Reply from 74.125.225.71: bytes=32 time=24ms TTL=55
Reply from 74.125.225.71: bytes=32 time=25ms TTL=55
Ping statistics for 74.125.225.71:
Packets: Sent = 2, Received = 2, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 24ms, Maximum = 25ms, Average = 24ms
Server: cdns01.comcast.net
Address: 75.75.75.75
Name: yahoo.com
Addresses: 206.190.36.45, 98.139.183.24, 98.138.253.109
Pinging yahoo.com [206.190.36.45] with 32 bytes of data:
Reply from 206.190.36.45: bytes=32 time=78ms TTL=49
Reply from 206.190.36.45: bytes=32 time=79ms TTL=49
Ping statistics for 206.190.36.45:
Packets: Sent = 2, Received = 2, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 78ms, Maximum = 79ms, Average = 78ms
Pinging 127.0.0.1 with 32 bytes of data:
Reply from 127.0.0.1: bytes=32 time<1ms TTL=64
Reply from 127.0.0.1: bytes=32 time<1ms TTL=64
Ping statistics for 127.0.0.1:
Packets: Sent = 2, Received = 2, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x2 ...00 1c c0 6f b7 48 ...... Intel® 82567LF-2 Gigabit Network Connection - Packet Scheduler Miniport
===========================================================================
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.1.100 192.168.1.112 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
192.168.1.0 255.255.255.0 192.168.1.112 192.168.1.112 20
192.168.1.112 255.255.255.255 127.0.0.1 127.0.0.1 20
192.168.1.255 255.255.255.255 192.168.1.112 192.168.1.112 20
224.0.0.0 240.0.0.0 192.168.1.112 192.168.1.112 20
255.255.255.255 255.255.255.255 192.168.1.112 192.168.1.112 1
Default Gateway: 192.168.1.100
===========================================================================
Persistent Routes:
None
========================= Winsock entries =====================================
Catalog5 01 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog5 02 C:\WINDOWS\system32\winrnr.dll [16896] (Microsoft Corporation)
Catalog5 03 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 01 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 02 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 03 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 04 C:\WINDOWS\system32\rsvpsp.dll [92672] (Microsoft Corporation)
Catalog9 05 C:\WINDOWS\system32\rsvpsp.dll [92672] (Microsoft Corporation)
Catalog9 06 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 07 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 08 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 09 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 10 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 11 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 12 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 13 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 14 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 15 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 16 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 17 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 18 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 19 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 20 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 21 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 22 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 23 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 24 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 25 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
Catalog9 26 C:\WINDOWS\system32\mswsock.dll [245248] (Microsoft Corporation)
**** End of log ****
In closing up this thread, I want to express my extreme gratitude to hero SleepyDude for sticking with me and trying to puzzle out this real weirdie!