Sweet a keeps restarting whenever I try to operate

Sweet a, or xtsi/505si in the west, keeps restarting whenever I try to operate it. If you leave it alone for a while it will function for a few times, but will restart again within a few operations, especially anything related to flash and shutter. Flash will immediately start a reboot, and a few shutter will do the same.What can it be? I doubt it's the capacitor. Do you guys know how to take it apart? Any service manual?