Hi do you get a blue screen (Bsod) if so please look in C:\windows\minidump.and copy the info there to a folder call it minidmp and attach to your next post someone will try to look at them for you to help track down the issue
Run msconfig and select the "Services" tab. Check "Hide Microsoft Services" and then disable the rest. Also uncheck "load startup items" on the general page.
Now restart and test the issue at hand
If no problems, run msconfig and recheck half the disabled items on the Services tab. Test again. If the problem recurs, UNcheck half the items you just checked to narrow down the culprit.
If the problem didn't occur, check the other half, so all the Services are enabled -- proceed to do this on the startup tab as well.
Get the idea? You want to isolate the problem to a specific startup if possible.
Note: if you already have items unchecked under msconfig > startups and are in “selective” startup mode – you should note what these are before beginning. They will need to be de-selected again.
http://support.microsoft.com/kb/929135/en-us >> writen for Vista but applies just as well to XP