Explorer.exe not loading on startup

What kind of antivirus are you using?

Symantec 10.1.5

I would try disabling symantec on one and see what happens.

Thank you for your response.
The problem is that the blue screen doesn't happen more than twice a week, some weeks it doesn't happen at all. I would be afraid to keep a PC without enabled virus protection for a week.

I would be worried that your systems are infected. Can you try another antivirus? How about post a hijackthis log?

By the way, sorry for the late response polanka. Lee if we get no response in 4 days you can close/refund.

My hijack log looks like this:

Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 11:49:26 AM, on 07/08/2008
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\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\Program Files\Common Files\Symantec Shared\ccSetMgr.exe
C:\Program Files\Common Files\Symantec Shared\ccEvtMgr.exe
C:\Program Files\Common Files\Symantec Shared\SPBBC\SPBBCSvc.exe
C:\WINDOWS\system32\spoolsv.exe
C:\Program Files\Common Files\Seagate\Schedule2\schedul2.exe
C:\Program Files\Lavasoft\Ad-Aware Enterprise Client\aaclient.exe
C:\Program Files\Intel\ASF Agent\ASFAgent.exe
C:\Program Files\Cisco Systems\VPN Client\cvpnd.exe
C:\Program Files\Symantec AntiVirus\DefWatch.exe
C:\Program Files\Intel\Intel Matrix Storage Manager\Iaantmon.exe
C:\Program Files\Common Files\Microsoft Shared\VS7DEBUG\MDM.EXE
C:\Program Files\Symantec AntiVirus\SavRoam.exe
C:\Program Files\Symantec AntiVirus\Rtvscan.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\hkcmd.exe
C:\WINDOWS\system32\igfxpers.exe
C:\WINDOWS\system32\igfxsrvc.exe
C:\Program Files\Common Files\Symantec Shared\ccApp.exe
C:\PROGRA~1\SYMANT~1\VPTray.exe
C:\WINDOWS\system32\ctfmon.exe
C:\Program Files\Danware Data\NetOp Remote Control\GUEST\Ngstw32.exe
C:\WINDOWS\system32\spool\drivers\w32x86\3\HPBPRO.EXE
C:\WINDOWS\system32\spool\drivers\w32x86\3\HPBOID.EXE
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\WISPTIS.EXE
C:\WINDOWS\system32\mstsc.exe
C:\Program Files\Microsoft Office\OFFICE11\OUTLOOK.EXE
C:\WINDOWS\system32\mstsc.exe
C:\Program Files\Crystal Decisions\Crystal Reports 10\crw32.exe
C:\Documents and Settings\user\Desktop\HiJackThis.exe
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = www.google.com/ig/dell?hl=en&client=dell-usuk-rel&channel=us&ibd=4071208 
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://www.dell.com 
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.dell.com 
R1 - HKLM\Software\Microsoft\Internet Explorer\Search,Default_Page_URL = www.google.com/ig/dell?hl=en&client=dell-usuk-rel&channel=us&ibd=4071208 
O2 - BHO: Adobe PDF Reader Link Helper - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Program Files\Common Files\Adobe\Acrobat\ActiveX\AcroIEHelper.dll
O2 - BHO: SSVHelper Class - {761497BB-D6F0-462C-B6EB-D4DAF1D92D43} - C:\Program Files\Java\jre1.6.0_05\bin\ssv.dll
O2 - BHO: AcroIEToolbarHelper Class - {AE7CD045-E861-484f-8273-0445EE161910} - C:\Program Files\Adobe\Acrobat 6.0\Acrobat\AcroIEFavClient.dll
O2 - BHO: PDF-XChange Viewer IE-Plugin - {C5D07EB6-BBCE-4DAE-ACBB-D13A8D28CB1F} - C:\Program Files\Tracker Software\PDF-XChange Viewer\pdf-viewer\PDFXCviewIEPlugin.dll
O2 - BHO: Browser Address Error Redirector - {CA6319C0-31B7-401E-A518-A07C3DB8F777} - C:\Program Files\BAE\BAE.dll
O3 - Toolbar: Adobe PDF - {47833539-D0C5-4125-9FA8-0819E2EAAC93} - C:\Program Files\Adobe\Acrobat 6.0\Acrobat\AcroIEFavClient.dll
O4 - HKLM\..\Run: [IgfxTray] C:\WINDOWS\system32\igfxtray.exe
O4 - HKLM\..\Run: [HotKeysCmds] C:\WINDOWS\system32\hkcmd.exe
O4 - HKLM\..\Run: [Persistence] C:\WINDOWS\system32\igfxpers.exe
O4 - HKLM\..\Run: [ccApp] "C:\Program Files\Common Files\Symantec Shared\ccApp.exe"
O4 - HKLM\..\Run: [vptray] C:\PROGRA~1\SYMANT~1\VPTray.exe
O4 - HKLM\..\Run: [Synchronization Manager] %SystemRoot%\system32\mobsync.exe /logon
O4 - HKCU\..\Run: [ctfmon.exe] C:\WINDOWS\system32\ctfmon.exe
O4 - HKCU\..\Run: [MSMSGS] "C:\Program Files\Messenger\msmsgs.exe" /background
O8 - Extra context menu item: E&xport to Microsoft Excel - res://C:\PROGRA~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_05\bin\ssv.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_05\bin\ssv.dll
O9 - Extra button: Research - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\OFFICE11\REFIEBAR.DLL
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
O16 - DPF: {6414512B-B978-451D-A0D8-FCFDF33E833C} (WUWebControl Class) - http://www.update.microsoft.com/windowsupdate/v6/V5Controls/en/x86/client/wuweb_site.cab?1199299187656 
O16 - DPF: {E06E2E99-0AA1-11D4-ABA6-0060082AA75C} (GpcContainer Class) - https://globalshopsolutions.webex.com/client/T25L/webex/ieatgpc.cab 
O17 - HKLM\System\CCS\Services\Tcpip\Parameters:
O17 - HKLM\Software\..\Telephony: DomainName =
O17 - HKLM\System\CS1\Services\Tcpip\Parameters:
O23 - Service: Acronis Scheduler2 Service (AcrSch2Svc) - Acronis - C:\Program Files\Common Files\Seagate\Schedule2\schedul2.exe
O23 - Service: Ad-Aware Enterprise Client - Unknown owner - C:\Program Files\Lavasoft\Ad-Aware Enterprise Client\aaclient.exe
O23 - Service: ASF Agent (ASFAgent) - Intel Corporation - C:\Program Files\Intel\ASF Agent\ASFAgent.exe
O23 - Service: Symantec Event Manager (ccEvtMgr) - Symantec Corporation - C:\Program Files\Common Files\Symantec Shared\ccEvtMgr.exe
O23 - Service: Symantec Settings Manager (ccSetMgr) - Symantec Corporation - C:\Program Files\Common Files\Symantec Shared\ccSetMgr.exe
O23 - Service: Cisco Systems, Inc. Installer service (CiscoVpnInstallService) - Unknown owner - D:\4.6\INSTAL~5.EXE (file missing)
O23 - Service: Commander Service - Seagull Scientific, Inc - C:\Program Files\Seagull\BarTender\7.74\CmdrSrv.exe
O23 - Service: Cisco Systems, Inc. VPN Service (CVPND) - Cisco Systems, Inc. - C:\Program Files\Cisco Systems\VPN Client\cvpnd.exe
O23 - Service: Symantec AntiVirus Definition Watcher (DefWatch) - Symantec Corporation - C:\Program Files\Symantec AntiVirus\DefWatch.exe
O23 - Service: dkab_device - - C:\WINDOWS\system32\DKabcoms.exe
O23 - Service: HP Port Resolver - Hewlett-Packard Company - C:\WINDOWS\system32\spool\drivers\w32x86\3\HPBPRO.EXE
O23 - Service: HP Status Server - Hewlett-Packard Company - C:\WINDOWS\system32\spool\drivers\w32x86\3\HPBOID.EXE
O23 - Service: Intel(R) Matrix Storage Event Monitor (IAANTMON) - Intel Corporation - C:\Program Files\Intel\Intel Matrix Storage Manager\Iaantmon.exe
O23 - Service: LiveUpdate - Symantec Corporation - C:\PROGRA~1\Symantec\LIVEUP~1\LUCOMS~1.EXE
O23 - Service: Pml Driver HPZ12 - HP - C:\WINDOWS\System32\spool\DRIVERS\W32X86\3\HPZipm12.exe
O23 - Service: SAVRoam (SavRoam) - symantec - C:\Program Files\Symantec AntiVirus\SavRoam.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: Symantec AntiVirus - Symantec Corporation - C:\Program Files\Symantec AntiVirus\Rtvscan.exe
--
End of file - 7435 bytes

Looks pretty clean to me, I still suspect Symantec... Can you uninstall/reinstall it on one machine to test? - or better yet, uninstall it, and try another AV (I'd just get a $30 one) on just one machine. This way you can rule out Symantec as the problem. Symantec can sometimes cause  weird incompatibilty problems with certain programs - some are resolved with a reinstall, some just dont work at all. I have substituted AVG or BitDefender for Symantec in these situations and resolved the problem. Not a guaranteed fix but that's where I'd try first

I would like to add that it's only accounts with admin rights that have that problem.