Pc Crashes

Its been getting better but I don't know how to solve it. When I start my computer it is very slow and my CPU usage goes very high. Then I try to play Team Fortress 2 and after a minute my CPU usage goes up to 80-100 percent and eventually my computer shuts off. When I start it, it says that it has closed with an error, like what happens when I hold down the power off button on the front of my pc. I had just done a complete system restore( reinstalled vista) about 2 weeks ago when I tried to install ubuntu and it installed over vista and I didnt have any backups. It was a clean reinstall. Please help this is so annoying.

PC SPECS:
Manufacturer: MY OWN CREATION
Processor: Intel® Core™2 Duo CPU E8400 @ 3.00GHz (2 CPUs), ~3.0GHz
Memory: 4094MB RAM
Hard Drive: 320 GB
Video Card: NVIDIA GeForce 8800 GT
Monitor: Generic PnP Monitor
Sound Card: Speakers (Realtek High Definition Audio)
Keyboard: USB Root Hub
Operating System: Windows Vista™ Ultimate (6.0, Build 6000) (6000.vista_gdr.071023-1545)
Motherboard: GIGABYTE GA-EP35-DS3L LGA 775 Intel P35 ATX Intel Motherboard
Computer Case: Antec sonata 3 with 500watt power supply

The following are the utility programs I ran on this PC to try and clean it up and speed it up as much as possible, but as I said, it's still VERY slow:

ATF Cleaner
Avast
Malwarebytes' Anti-Malware
Spybot Search and Destroy
Defragment - Defragmented entire C: drive

Can someone please take a look at this report and let me know what I should do next?

Below is the HijackThis log:

(((((((((( HijackThis Log ))))))))))

Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 6:36:28 PM, on 3/3/2009
Platform: Windows Vista SP1 (WinNT 6.00.1905)
MSIE: Internet Explorer v7.00 (7.00.6001.18000)
Boot mode: Normal

Running processes:
C:\Program Files (x86)\Spybot - Search & Destroy\TeaTimer.exe
C:\Program Files (x86)\Steam\Steam.exe
C:\Program Files (x86)\Xfire\Xfire.exe
C:\Program Files\Alwil Software\Avast4\ashDisp.exe
C:\Program Files (x86)\Opera\Opera.exe
C:\Users\John\Desktop\HiJackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft....k/?LinkId=54896
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://go.microsoft....k/?LinkId=69157
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://go.microsoft....k/?LinkId=69157
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://go.microsoft....k/?LinkId=54896
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft....k/?LinkId=54896
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://go.microsoft....k/?LinkId=69157
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,SearchAssistant =
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,CustomizeSearch =
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName =
F2 - REG:system.ini: UserInit=userinit.exe
O1 - Hosts: ::1 localhost
O2 - BHO: Spybot-S&D IE Protection - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~2\SPYBOT~1\SDHelper.dll
O4 - HKLM\..\Run: [QuickTime Task] "C:\Program Files (x86)\QuickTime\QTTask.exe" -atboottime
O4 - HKLM\..\Run: [avast!] C:\PROGRA~1\ALWILS~1\Avast4\ashDisp.exe
O4 - HKCU\..\Run: [WindowsWelcomeCenter] rundll32.exe oobefldr.dll,ShowWelcomeCenter
O4 - HKCU\..\Run: [SpybotSD TeaTimer] C:\Program Files (x86)\Spybot - Search & Destroy\TeaTimer.exe
O4 - HKCU\..\Run: [Steam] "C:\Program Files (x86)\Steam\Steam.exe" -silent
O4 - HKUS\S-1-5-19\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /detectMem (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-19\..\Run: [WindowsWelcomeCenter] rundll32.exe oobefldr.dll,ShowWelcomeCenter (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-20\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /detectMem (User 'NETWORK SERVICE')
O4 - Startup: Xfire.lnk = C:\Program Files (x86)\Xfire\Xfire.exe
O9 - Extra button: Research - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~2\MICROS~1\OFFICE11\REFIEBAR.DLL
O9 - Extra button: (no name) - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~2\SPYBOT~1\SDHelper.dll
O9 - Extra 'Tools' menuitem: Spybot - Search & Destroy Configuration - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~2\SPYBOT~1\SDHelper.dll
O13 - Gopher Prefix:
O16 - DPF: {D27CDB6E-AE6D-11CF-96B8-444553540000} (Shockwave Flash Object) - http://fpdownload2.m...ash/swflash.cab
O18 - Protocol: skype4com - {FFC8B962-9B40-4DFF-9458-1830C7DD7F5D} - C:\PROGRA~2\COMMON~1\Skype\SKYPE4~1.DLL
O23 - Service: @%SystemRoot%\system32\Alg.exe,-112 (ALG) - Unknown owner - C:\Windows\System32\alg.exe (file missing)
O23 - Service: avast! iAVS4 Control Service (aswUpdSv) - ALWIL Software - C:\Program Files\Alwil Software\Avast4\aswUpdSv.exe
O23 - Service: avast! Antivirus - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashServ.exe
O23 - Service: avast! Mail Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe
O23 - Service: avast! Web Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashWebSv.exe
O23 - Service: @dfsrres.dll,-101 (DFSR) - Unknown owner - C:\Windows\system32\DFSR.exe (file missing)
O23 - Service: @%systemroot%\system32\fxsresm.dll,-118 (Fax) - Unknown owner - C:\Windows\system32\fxssvc.exe (file missing)
O23 - Service: {4FE82739-F5B8-408C-BB9A-6424344CF8C0} (iioikbw) - Unknown owner - C:\Program Files (x86)\ophcrack\pwdump\servpw.exe
O23 - Service: @keyiso.dll,-100 (KeyIso) - Unknown owner - C:\Windows\system32\lsass.exe (file missing)
O23 - Service: @comres.dll,-2797 (MSDTC) - Unknown owner - C:\Windows\System32\msdtc.exe (file missing)
O23 - Service: @%SystemRoot%\System32\netlogon.dll,-102 (Netlogon) - Unknown owner - C:\Windows\system32\lsass.exe (file missing)
O23 - Service: NVIDIA Display Driver Service (nvsvc) - Unknown owner - C:\Windows\system32\nvvsvc.exe (file missing)
O23 - Service: @%systemroot%\system32\psbase.dll,-300 (ProtectedStorage) - Unknown owner - C:\Windows\system32\lsass.exe (file missing)
O23 - Service: @%systemroot%\system32\Locator.exe,-2 (RpcLocator) - Unknown owner - C:\Windows\system32\locator.exe (file missing)
O23 - Service: @%SystemRoot%\system32\samsrv.dll,-1 (SamSs) - Unknown owner - C:\Windows\system32\lsass.exe (file missing)
O23 - Service: SBSD Security Center Service (SBSDWSCService) - Safer Networking Ltd. - C:\Program Files (x86)\Spybot - Search & Destroy\SDWinSec.exe
O23 - Service: @%SystemRoot%\system32\SLsvc.exe,-101 (slsvc) - Unknown owner - C:\Windows\system32\SLsvc.exe (file missing)
O23 - Service: @%SystemRoot%\system32\snmptrap.exe,-3 (SNMPTRAP) - Unknown owner - C:\Windows\System32\snmptrap.exe (file missing)
O23 - Service: @%systemroot%\system32\spoolsv.exe,-1 (Spooler) - Unknown owner - C:\Windows\System32\spoolsv.exe (file missing)
O23 - Service: Steam Client Service - Valve Corporation - C:\Program Files (x86)\Common Files\Steam\SteamService.exe
O23 - Service: @%SystemRoot%\system32\ui0detect.exe,-101 (UI0Detect) - Unknown owner - C:\Windows\system32\UI0Detect.exe (file missing)
O23 - Service: @%SystemRoot%\system32\vds.exe,-100 (vds) - Unknown owner - C:\Windows\System32\vds.exe (file missing)
O23 - Service: @%systemroot%\system32\vssvc.exe,-102 (VSS) - Unknown owner - C:\Windows\system32\vssvc.exe (file missing)
O23 - Service: @%systemroot%\system32\wbengine.exe,-104 (wbengine) - Unknown owner - C:\Windows\system32\wbengine.exe (file missing)
O23 - Service: @%Systemroot%\system32\wbem\wmiapsrv.exe,-110 (wmiApSrv) - Unknown owner - C:\Windows\system32\wbem\WmiApSrv.exe (file missing)
O23 - Service: @%ProgramFiles%\Windows Media Player\wmpnetwk.exe,-101 (WMPNetworkSvc) - Unknown owner - C:\Program Files (x86)\Windows Media Player\wmpnetwk.exe (file missing)

--
End of file - 6369 bytes