Then it is the most likely, fuse or regulator, a simple multimeter check on the fuse will show you if that's the problem, if the fuse is ok, then check regulator (7805), middle leg is ground the outer is in and the other is out, it should leave 5v, not 4v not 6v, +-0,2v is ok.
And you will need a 4.5mm gamebit to get it open too...