Last two times I have booted my computer up it takes me to the screen where you select what mode to run it in. Then usually takes a couple more screens of scans and loads before it boots up. Has restarted twice for no reason while I am on it. I ran hijackthis just in case and here is the log.

Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 3:57:57 PM, on 9/4/2008
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)
Boot mode: Normal

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\system32\Ati2evxx.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
c:\Program Files\Common Files\Symantec Shared\ccProxy.exe
c:\Program Files\Common Files\Symantec Shared\ccSetMgr.exe
c:\Program Files\Norton Internet Security\ISSVC.exe
c:\Program Files\Common Files\Symantec Shared\SNDSrvc.exe
c:\Program Files\Common Files\Symantec Shared\SPBBC\SPBBCSvc.exe
C:\WINDOWS\system32\Ati2evxx.exe
c:\Program Files\Common Files\Symantec Shared\ccEvtMgr.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\spoolsv.exe
C:\Program Files\Common Files\Microsoft Shared\VS7DEBUG\MDM.EXE
c:\Program Files\Norton Internet Security\Norton AntiVirus\navapsvc.exe
C:\WINDOWS\system32\svchost.exe
c:\Program Files\Common Files\Symantec Shared\Security Center\SymWSC.exe
C:\Program Files\Common Files\Symantec Shared\ccApp.exe
C:\Program Files\HP\HP Software Update\HPwuSchd2.exe
C:\WINDOWS\system32\ctfmon.exe
C:\Program Files\Google\GoogleToolbarNotifier\1.2.1128.5462\GoogleToolbarNotifier.exe
C:\Program Files\AIM\aim.exe
C:\Program Files\Compaq Connections\5577497\Program\Compaq Connections.exe
C:\WINDOWS\system32\wuauclt.exe
C:\HP\KBD\KBD.EXE
C:\WINDOWS\RTHDCPL.EXE
C:\Program Files\ATI Technologies\ATI Control Panel\atiptaxx.exe
C:\Program Files\Mozilla Firefox\firefox.exe
c:\windows\system\hpsysdrv.exe
C:\Program Files\Java\jre1.5.0_05\bin\jusched.exe
C:\Documents and Settings\Compaq_Administrator\Desktop\HiJackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = https://login.yahoo.com/config/login.../www.yahoo.com
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Bar = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
R1 - HKCU\Software\Microsoft\Internet Connection Wizard,ShellNext = http://ie.redirect.hp.com/svs/rdr?TY...rio&pf=desktop
O2 - BHO: AcroIEHlprObj Class - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Program Files\Adobe\Acrobat 7.0\ActiveX\AcroIEHelper.dll
O2 - BHO: Google Toolbar Helper - {AA58ED58-01DD-4d91-8333-CF10577473F7} - c:\program files\google\googletoolbar3.dll
O2 - BHO: NAV Helper - {BDF3E430-B101-42AD-A544-FADC6B084872} - c:\Program Files\Norton Internet Security\Norton AntiVirus\NavShExt.dll
O3 - Toolbar: Norton AntiVirus - {42CDD1BF-3FFB-4238-8AD1-7859DF00B1D6} - c:\Program Files\Norton Internet Security\Norton AntiVirus\NavShExt.dll
O3 - Toolbar: &Google - {2318C2B1-4965-11d4-9B18-009027A5CD4F} - c:\program files\google\googletoolbar3.dll
O4 - HKLM\..\Run: [ccApp] "c:\Program Files\Common Files\Symantec Shared\ccApp.exe"
O4 - HKLM\..\Run: [URLLSTCK.exe] c:\Program Files\Norton Internet Security\UrlLstCk.exe
O4 - HKLM\..\Run: [HPBootOp] "C:\Program Files\Hewlett-Packard\HP Boot Optimizer\HPBootOp.exe" /run
O4 - HKLM\..\Run: [HP Software Update] C:\Program Files\HP\HP Software Update\HPwuSchd2.exe
O4 - HKLM\..\Run: [TkBellExe] "C:\Program Files\Common Files\Real\Update_OB\realsched.exe" -osboot
O4 - HKLM\..\Run: [KernelFaultCheck] %systemroot%\system32\dumprep 0 -k
O4 - HKCU\..\Run: [ctfmon.exe] C:\WINDOWS\system32\ctfmon.exe
O4 - HKCU\..\Run: [swg] C:\Program Files\Google\GoogleToolbarNotifier\1.2.1128.5462\GoogleToolbarNotifier.exe
O4 - HKCU\..\Run: [AIM] C:\Program Files\AIM\aim.exe -cnetwait.odl
O4 - .DEFAULT User Startup: Pin.lnk = C:\hp\bin\CLOAKER.EXE (User 'Default user')
O4 - Startup: Adobe Gamma.lnk = C:\Program Files\Common Files\Adobe\Calibration\Adobe Gamma Loader.exe
O4 - Startup: Compaq Organize.lnk = ?
O4 - Global Startup: Compaq Connections.lnk = C:\Program Files\Compaq Connections\5577497\Program\Compaq Connections.exe
O4 - Global Startup: HP Digital Imaging Monitor.lnk = C:\Program Files\HP\Digital Imaging\bin\hpqtra08.exe
O4 - Global Startup: Microsoft Office.lnk = C:\Program Files\Microsoft Office\Office\OSA9.EXE
O8 - Extra context menu item: E&xport to Microsoft Excel - res://C:\PROGRA~1\MICROS~4\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.5.0_05\bin\npjpi150_05.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.5.0_05\bin\npjpi150_05.dll
O9 - Extra button: Research - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~4\OFFICE11\REFIEBAR.DLL
O9 - Extra button: AIM - {AC9E2541-2814-11d5-BC6D-00B0D0A1DE45} - C:\Program Files\AIM\aim.exe
O9 - Extra button: Connection Help - {E2D4D26B-0180-43a4-B05F-462D6D54C789} - C:\WINDOWS\PCHEALTH\HELPCTR\Vendors\CN=Hewlett-Packard,L=Cupertino,S=Ca,C=US\IEButton\support.htm
O9 - Extra 'Tools' menuitem: Connection Help - {E2D4D26B-0180-43a4-B05F-462D6D54C789} - C:\WINDOWS\PCHEALTH\HELPCTR\Vendors\CN=Hewlett-Packard,L=Cupertino,S=Ca,C=US\IEButton\support.htm
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O23 - Service: Ati HotKey Poller - ATI Technologies Inc. - C:\WINDOWS\system32\Ati2evxx.exe
O23 - Service: Symantec Event Manager (ccEvtMgr) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\ccEvtMgr.exe
O23 - Service: Symantec Network Proxy (ccProxy) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\ccProxy.exe
O23 - Service: Symantec Password Validation (ccPwdSvc) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\ccPwdSvc.exe
O23 - Service: Symantec Settings Manager (ccSetMgr) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\ccSetMgr.exe
O23 - Service: Google Updater Service (gusvc) - Google - C:\Program Files\Google\Common\Google Updater\GoogleUpdaterService.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Program Files\Common Files\InstallShield\Driver\1050\Intel 32\IDriverT.exe
O23 - Service: ISSvc (ISSVC) - Symantec Corporation - c:\Program Files\Norton Internet Security\ISSVC.exe
O23 - Service: Norton AntiVirus Auto-Protect Service (navapsvc) - Symantec Corporation - c:\Program Files\Norton Internet Security\Norton AntiVirus\navapsvc.exe
O23 - Service: SAVScan - Symantec Corporation - c:\Program Files\Norton Internet Security\Norton AntiVirus\SAVScan.exe
O23 - Service: Symantec Network Drivers Service (SNDSrvc) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\SNDSrvc.exe
O23 - Service: Symantec SPBBCSvc (SPBBCSvc) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\SPBBC\SPBBCSvc.exe
O23 - Service: SymWMI Service (SymWSC) - Symantec Corporation - c:\Program Files\Common Files\Symantec Shared\Security Center\SymWSC.exe

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End of file - 8051 bytes

I think you have a virus (Ati2evxx.exe).
Print and follow these steps and you should have it fixed.
1.Download ComboFix from here and save it to your desktop.
2.Backup files you need/do a backup for your precious data.
3.Exit all programs and disconnect physically from the internet(disconnect the cable)
4.Start ComboFix,type 1 and press enter
5.Don't use the computer until ComboFix finishes.
6.When ComboFix finishes, exit and reconnect to the Internet.
7.Post the content of C:\ComboFix.txt here.