If this is a recent issue, try using System Restore to take you back to a
time prior to when this began.
If that doesn't resolve it, be sure your antivirus software has the latest
definitions and run a
virus scan.
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.
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. No 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.
Also, download, install and run Ad Aware:
www.lavasoftusa.com