Have you checked your PSU rails? Either in the BIOS or using Speed Fan.
With the numerous unistalls and reinstall of drivers and such, I would recommend that you use CCleaner to remove any incorrect registry files. Some more ideas are to run an anti virus, and spyware cleaner and make sure it not that which is causing your reboots. Have you looked for any recent motherboard drivers? Drivers for the chipsets and any on board devices that you are use?
Hopefully something helps.