Couple 'first guess' possibilities:
Have you done the (obligatory) "Load Optimized Defaults" from the BIOS? If not, do so...
What in the way of USB devices have you got plugged in? GB's have a well-known 'pickiness' about some USB stuff; I've never heard of either a ketboard or mouse causing this problem, but I've seen it with: external hard-drives, external CD/DVD writers, various brands of pen drives, and, I think I recall, someones brand of MP3 player... Reboot loops are the most common symptom. On theBIOS' "Integrated Peripherals" page, set "Legacy USB storage detect" (later BIOS say "USB Storage Function") - either way, set it to "Disabled"... If you still get looping with all USBs out, and that setting made, try this:
While it's in the loop, hold the power button depressed for long enough to get it to shut down completely. Turn off the power supply at the PSU swith, or unplug it. Do a CMOS reset, while it's off, or unplugged. Assuming you've gotten rid of the cause (no extraneous USBs, and the setting above corrected), you should be able to power up - do the 'Load Optimized' again, and you should be good to go...