Is this a new problem? Were things working OK previously? Any new hardware or software?
If this is a new problem try a System Restore to a point prior to the problem:
start > All Programs > Accessories > System Tools > System Restore
If that doesn't help look in your Event viewer: rt. click My Computer then click Manage then Event Viewer.
Or: Administrative Tools/Event Viewer or Start/Run/ eventvwr
Open the system as well as the application tabs & look for red
X errors. Click error line for details.
Post back the source & event id & Description especially of errors that seem to coincide with this issue.
Also check the Information lines that might coincide with this issue.
How to view and manage event logs in Event Viewer in Windows XP
If you see any error details such as EVENT_SHELL_RESTARTED then:
Try this little app:
http://www.snapfiles.com/get/shellexview.html
First off see what items come up red tagged or pink.
Another common trigger to this error is Google Toolbar. If you have it remove it.
If none of the above helps then:
As a first response you might want to post a HijackThis log for review by our Pros in that section:
Please follow the instructions
HERE & then post your log in a new thread in the
Spyware, Adware, Viruses and HijackThis Logs section.
(Not in this section please).
Please specify what issues you appear to be experiencing along with your log.