Unable to boot into Win 2000 Op. System

I have a compaq 5716 Presario which I updated to windows 2000 from Windows 98. The upgrade was a success. I installed a Driver for the Compaq DVD player, and now the computer does not boot into the Op system. The system boots to a point, then as it gets to go to the desktop, it reboots. How can I fix this problem? I tried to boot into safe mode, etc, nothing works.