What happens when you start in Safe mode?
Here are some tips from the forums.
If 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: 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.