Used AV8 Problem

I need some help w/ the codes too. I just bought the AV8 used from a friend. However, after installing it, the red power LED flashes for a brief second and then the whole system shuts down. It gives me an "F." code. Then, it will spontaneously spin up for about 10 seconds, then shuts off, with what looks like "9.C.". I think it's just a shorted-out mobo, but I'm hoping for the best. Any help would be appreciated, thanks.