You're welcome.
There are many possibilities and no simple answer.
Once you get yourself squared away, first thing I would suggest is to use
the tools disk that came with your hard drive and run a diagnostic. If you
don't have that disk, go to the hard drive manufacturer's website and
download the tools there. These diagnostic tools will do a much more robust
and thorough check of your hard drive's health than any tools included with
Windows.
If all is well, run regular scans of your system with up to date antivirus
software. These applications have regular updates and you should scan your
system after each one to be sure nothing came in to your system before the
update. This software is not just a gateway but too many users only use it
in that regard. Your system needs to be scanned regularly. Viruses can
cause problems with files, can corrupt files and cause the problem you
experienced.
Make sure the drivers for all of your hardware is up to date and that you
check regularly for new drivers. Problem or outdated drivers can crash your
system and crashes, hangs, shutdowns, etc. can cause problems such as you
experienced. Make sure your software and hardware is all XP compatible.
Download XP's Update advisor and run it, it will look for any problem
hardware or software on your system:
http://www.microsoft.com/windowsxp/pro/howtobuy/upgrading/advisor.asp
If your system is new, don't assume everything is compatible, we are in a
fast changing environment and sometime things are dated by release. It's
quite common by the way for people to purchase a new device and assume the
drivers have not been updated. Unfortunately, there's no way to tell how
long the device has been on the shelf or in a warehouse and in that period,
new drivers may have been released and they often solve problems many users
face.
Check the error log, double click any errors you find, the information
contained within might point to the source of some problem. Open Control
Panel, open Administrative Tools, open Event Viewer and check all sections
in the viewer for error messages. Some may be meaningless, others may well
point to recurring problems on your system that might be the source of this
issue.
Also, download, install and run Ad Aware:
www.lavasoftusa.com.
If you have any spyware on your system, this application can help find it.
Again, such spyware can be the source of the type of problem you describe.