Open Control Panel, open Administrative Tools, open Event Viewer, look for
errors that correspond to when the problem occurs, double click the error,
the information contained within may give a clue as to the source of the
error.
Make sure your drivers are up to date, especially for your graphics card,
soundcard and any peripherals connected tot he system. Go to the device
manufacturer's web sites for this not to Windows Update.
Place the XP CD in the drive, when the setup screen appears, select "Check
System Compatibility." The report it generates may give a clue as to
problem areas on your system, areas that might be the source of the issue.
If you have a recovery CD as opposed to a Windows CD, you can download the
upgrade advisor from the following web site:
http://www.microsoft.com/windowsxp/pro/howtobuy/upgrading/advisor.asp