First, be sure your antivirus software has the latest definitions and run a
virus scan.

Second, download, install and run Ad Aware:
www.lavasoftusa.com
Note: you should always be well backed up before running an application of
this type.

If your system is clear of viruses, open Control Panel, open System, go to
the Advanced tab, click Settings under Startup and Recovery, remove the
check from "Automatically Restart" under System Failure.  This will cause
the system to blue screen instead of restarting on errors and the
information on the blue screen may give a clue as to the source of the
issue.

Open Control Panel, open Administrative Tools, open Event Viewer, look for
errors corresponding to the crash, double click the error, the information
contained within may give a clue as to the
source of the problem.  If you don't understand the information inside, the
third button down in that dialog box will copy the information,
you can then paste it into a message and post it here and maybe we can
figure out what is going on.

Assuming you have an XP CD and not a recovery CD, place the XP CD in the
drive, when the setup screen appears, select "Check System Compatibility,"
the report it generates may point to problem hardware or software on your
system.  If you do not have an XP CD, you can download this application
known as the Upgrade Advisor from the following site:
http://www.microsoft.com/windowsxp/pro/howtobuy/upgrading/advisor.asp
Note: If you have access to a broadband connection it might be best to
download using that as this is a rather large download.

Check for the latest drivers for your hardware, especially your graphics
card and soundcard and all peripherals connected to your system.  Do not use
Windows Update for this, go to the device manufacturer's web sites and if
you install updated drivers, ignore the message about drivers being unsigned
by Microsoft.  *Before installing any drivers, be sure you are well backed
up and it's probably a good idea to manually create a restore point in
System Restore in case you have problems as a result of the driver update
and note, System Restore is not a substitute for a backup.  Start\All
Programs\Accessories\System Tools\System Restore