From what I understand about your (physical) setup, you're no longer connected via a router, correct? Are you simply attempting to connect directly to your modem now (without any sort of a network; ie: you're only attempting to connect one computer to your modem)? If so, please try the following:
(With only your LAC connected)
1. Start Control Panel, select Network and Internet Connections. Select 'Set up..' This will open the Internet Properties window.
2. Choose 'Connect to the Internet'.
3. Select 'Set up my connection manually'.
4. Choose your connection type, and press next.
5. Enter your DNS' name.
6. Enter your Username, Password (confirm password), and check the options below confirm password.
7. Select 'Add a short-cut to my Desktop'.
Now, attempt to connect with your new Connection (without the PPP connected).
If there's no change, then please try the following:
First, connect your PPP connection, ensure it's operating properly, and then goto Start, Run, CMD, and then type IPCONFIG /ALL.
Please copy down the following details (in a text file or on a piece of paper) -
The IP Address, the Subnet Mask, Default Gateway, and two of your DNS Server Addresses.
Now, do the following (please disconnect your PPP connection, so that only your LAC is connected):
1. Right-click on your 'My Network Connections' and select 'Properties'.
2. Right-click on your 'Local Area Connection' and select 'Properties'.
3. Select 'Internet Protocol (TCP/IP)', now click on the 'Properties' button.
4. Under the 'General' tab, select 'Use the following IP Address'.
5. Enter the necessary details in the following fields (exactly the same as those that you wrote down earlier).
6. Now, select 'Use the following DNS server addresses' and enter the two DNS Addresses.
Press 'OK' and then restart your computer and attempt to connect to the internet. If you cannot connect, then return to your TCP/IP Properties by followings Steps 1-3, and then return your options to 'Obtain an IP Address automatically' and 'Obtain DNS Servers automatically', restart your computer.
Let me know how you went.