|well,not much will happen if you remove EVERYTHING except the mobo, but you can strip it down quite a bit:|
remove all drives (hard, optical, and floppy)
remove all PCI cards (network, sound, etc)
remove all but one stick of RAM
you should leave only the mobo, psu, cpu, ram, and video.
without any HDDs, you won't be able to boot into Windows, but you should be able to get into the Bios. if the PC is still rebooting like before with this configuration, you can try a different stick of ram. if you're still getting the same behavior, you've isolated the problem down to PSU, mobo, or CPU.