Changed BIOS settings to default, now blue error screen, hard drive not found

[s.and]

I am running Windows XP Pro on an Nspire laptop purchased just a few months back.  I installed Ad Aware, Spybot Search & Destroy, Spyblaster, Windows Defender, and Zone Alarm in addition to the Verizon Security Suite that was currently running in order to find and delete some adware viruses.  Spybot was successful and everything was restored to normal for a couple of days until I restarted and got a blue screen error "IRQL_NOT_LESS_OR_EQUAL" and stating that I should disable BIOS memory options.  I assumed that I had too many virus scanning programs and firewalls installed so I was able to boot into safe mode as administrator and deleted all of the before mentioned programs except for Windows Defender and Verizon Security Suite which I planned to keep.  At restart I received the same blue screen message so I went to the BIOS setup menu to check the memory options and my BIOS menu has extremely limited settings options (Phoenix Trusted Core) which frustrated me and I (stupidly) reset the default settings.  Now I was unable to get past the black screen telling me that Windows failed to start normally.  So I went to the XP recovery CD and tried recovery and now all I get is a blue screen saying hard drive not found. 
This laptop was purchased "Vista ready" but with XP Pro installed by my request.  Could the problem possibly be that XP setup is not recognizing the hard drive because I reset the settings to default and now the hard drive is recognizable by Vista but not by XP?   
Sorry for such a long message but alot happened at once and I assumed the more info the better.
Thanks in advance!

[s.and]

I believe I have narrowed it down to a Windows software problem.  I disabled AHCI Configuration and Windows rebooted fine with all programs and documents still in place.  And then after a few minutes, blue screen.  The same error message as before: IRQL_NOT_LESS_OR_EQUAL and stating that I need to disable bios memory options such as caching or shadowing.  I believe that the bios is fine but that some software is messing everything up.  I will do further investigation.

[s.and]

I ran a scan with iobit and allowed it to fix a lot of problems with the registry, 200+ which involved MRU cache.  After, I restarted and all is normal, no crashes, no "Windows has just recovered from error" message, Internet is restored.  I have restarted quite a few times now and everything appears normal.  I'm "thinking happy thoughts"!