Sometimes, if you click to send the error report, then view details, it will load a page in your browser that may give some idea what is happening.
Have a look in Event Viewer to see if there are any erros at the time of crashes:
Right-click My Computer > Manage.
Click the + to the left of Event Viewer, then Click System. Look for any errors. Double-click on each one, then click the hyperlink to see if it helps you.
If still no clues, your RAM would be next thing to check. If you have more than 1, take 1 out and run the computer again. If it still crashes, swap them over and try again.
-------------------- OK OK I can't go any faster! aaaaaaaaaaaagh!