Buenas, Desde ya muchas gracias por la ayuda que me puedan brindar.
Cuando aparece el escritorio en la pantalla se reinicia. Aca les dejo el Log.

Logfile of HijackThis v1.99.1
Scan saved at 08:59:09 p.m., on 21/05/2007
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v7.00 (7.00.5730.0011)

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\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\ctfmon.exe
C:\Archivos de programa\Internet Explorer\iexplore.exe
C:\Archivos de programa\HJT\HijackThis.exe

R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://go.microsoft.com/fwlink/?LinkId=69157
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://go.microsoft.com/fwlink/?LinkId=54896
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft.com/fwlink/?LinkId=54896
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://go.microsoft.com/fwlink/?LinkId=69157
R1 - HKCU\Software\Microsoft\Windows\CurrentVersion\Int ernet Settings,ProxyServer = 200.100.100.7:6588
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Vínculos
F3 - REG:win.ini: run=C:\WINDOWS\ServicePackFiles\services.exe
O2 - BHO: AcroIEHlprObj Class - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Archivos de programa\Adobe\Acrobat 7.0\ActiveX\AcroIEHelper.dll
O2 - BHO: (no name) - {7E853D72-626A-48EC-A868-BA8D5E23E045} - (no file)
O4 - HKLM\..\Run: [KernelFaultCheck] %systemroot%\system32\dumprep 0 -k
O4 - HKCU\..\Run: [System update] C:\DOCUME~1\Alex\CONFIG~1\Temp\1670.exe
O4 - HKCU\..\Run: [ctfmon.exe] C:\WINDOWS\system32\ctfmon.exe
O8 - Extra context menu item: E&xportar a Microsoft Excel - res://C:\ARCHIV~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {85d1f590-48f4-11d9-9669-0800200c9a66} - %windir%\bdoscandel.exe (file missing)
O9 - Extra 'Tools' menuitem: Uninstall BitDefender Online Scanner v8 - {85d1f590-48f4-11d9-9669-0800200c9a66} - %windir%\bdoscandel.exe (file missing)
O9 - Extra button: Referencia - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\ARCHIV~1\MICROS~2\OFFICE11\REFIEBAR.DLL
O9 - Extra button: (no name) - {e2e2dd38-d088-4134-82b7-f2ba38496583} - %windir%\Network Diagnostic\xpnetdiag.exe (file missing)
O9 - Extra 'Tools' menuitem: @xpsp3res.dll,-20001 - {e2e2dd38-d088-4134-82b7-f2ba38496583} - %windir%\Network Diagnostic\xpnetdiag.exe (file missing)
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Archivos de programa\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Archivos de programa\Messenger\msmsgs.exe
O11 - Options group: [INTERNATIONAL] International*
O15 - Trusted Zone: http://update.microsoft.com.
O16 - DPF: {0EB0E74A-2A76-4AB3-A7FB-9BD8C29F7F75} (CKAVWebScan Object) - http://www.kaspersky.com/kos/english/kavwebscan_unicode.cab
O16 - DPF: {17492023-C23A-453E-A040-C7C580BBF700} (Windows Genuine Advantage Validation Tool) - http://go.microsoft.com/fwlink/?linkid=39204
O16 - DPF: {193C772A-87BE-4B19-A7BB-445B226FE9A1} (ewidoOnlineScan Control) - http://download.ewido.net/ewidoOnlineScan.cab
O16 - DPF: {4F1E5B1A-2A80-42CA-8532-2D05CB959537} (MSN Photo Upload Tool) - http://by122fd.bay122.hotmail.msn.com/resources/MsnPUpld.cab
O16 - DPF: {5D86DDB5-BDF9-441B-9E9E-D4730F4EE499} (BDSCANONLINE Control) - http://www.bitdefender-es.com/scan8/oscan8.cab
O16 - DPF: {6E32070A-766D-4EE6-879C-DC1FA91D2FC3} (MUWebControl Class) - http://update.microsoft.com/microsoftupdate/v6/V5Controls/en/x86/client/muweb_site.cab?1155613304328
O16 - DPF: {6E5A37BF-FD42-463A-877C-4EB7002E68AE} (Housecall ActiveX 6.5) - http://eu-housecall.trendmicro-europe.com/housecall/applet/html/native/x86/win32/activex/hcImpl.cab
O16 - DPF: {74CD40EA-EF77-4BAD-808A-B5982DA73F20} - http://yax-download.yazzle.net/YazzleActiveX.cab?refid=1123
O16 - DPF: {D7BF3304-138B-4DD5-86EE-491BB6A2286C} - http://www.azebar.com/1/sux.cab
O18 - Protocol: livecall - {828030A1-22C1-4009-854F-8E305202313F} - C:\ARCHIV~1\MSNMES~1\MSGRAP~1.DLL
O18 - Protocol: msnim - {828030A1-22C1-4009-854F-8E305202313F} - C:\ARCHIV~1\MSNMES~1\MSGRAP~1.DLL
O20 - Winlogon Notify: rpcc - C:\WINDOWS\system32\rpcc.dll
O21 - SSODL: WPDShServiceObj - {AAA288BA-9A4C-45B0-95D7-94D524869DB5} - C:\WINDOWS\system32\WPDShServiceObj.dll
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Archivos de programa\Archivos comunes\InstallShield\Driver\11\Intel 32\IDriverT.exe
O23 - Service: NOD32 Kernel Service (NOD32krn) - Unknown owner - C:\Archivos de programa\Eset\nod32krn.exe