If you find that your Dreamcast is constantly reseting there is an easy fix for this. What has happened is that there is a bad connection between the power supply and the rest of the system. This can be from either bent contact pins or oxidation. Open up the system and remove the power supply PCB. Bend the pins in the contact so that they will be tighter and clean the pins from the system board with rubbing alcohol or even a bit of sanding paper, reassemble and it should not restart anymore.