What happens if you boot in safe mode?

I would identify the brand of hard drive, go to the maker's web site,
download their diagnostic software and check the health of the drive.

first thing i do when people bring me their pc's with
screwball problems is ask the question to which i already
know the answer,and that is,do they run an updated Anti-
Virus program.99% of the time,the answer is a lowered
head "no".I just had one with XP that would bump them off
the Net and reboot,It had the Sasser,Blaster and Welchia
worms,and the XP software was never updated with security
patches.I would try to get into safe mode,and if you can
go online,go to the Symantec or Mcafee site and have them
run a scan on your system before proceeding
further.Spyware is another thing that can really screw
things up.If you don't already have them,i would download
both Spybots and Ad-Aware fro PCWorld.com and see what
they find.I try to take care of the basics first before i
go crazy troubleshooting these type of problems.Hope this
helps.

I had the same problem just last week and this was the
response I got,try it, it worked for me.

I suggest that you remove Temporary Internet Files (
including Offline Content ) and History. Start Settings,
Control Panel, Internet Options, General, Temporary
Internet Files, Delete Files, check Offline Content and
click on OK. Also empty  your Recycle Bin. This helps
remove a potential problem when running Scandisk and Disk
Defragmenter.

Another precaution. Delete the contents of the applog
folder ( the content not the folder! ). See link below
(disregard the references to the error messages ) for the
procedure.

Defrag Error Message: ID No:DEFRAG00205 (Q238165)
http://support.microsoft.com/default.aspx?scid=kb;en-
us;Q238165

Then run Disk Defragmenter in Safe Mode.

To start Windows in safe mode Click Start, and then click
Shut down. Click Restart, click OK, and then press and
hold the CTRL key until the Microsoft Windows 98 Start-up
Menu appears. For some machines, you can use F8 instead of
CTRL to bring up the Microsoft Windows 98 Start-up Menu.
Enter the number for Safe mode, and then press ENTER.

Notes In safe mode, Windows uses default settings (VGA
monitor, no network, Microsoft mouse driver, and the
minimum device drivers required to start Windows). You
will not have access to CD-ROM drives, printers, or other
devices.

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Hope this helps.