If U8 is bad you should still get some blinking. You can pull the chip off of the board and try the flash sequence, but its probably not causing the lock up.
Those masked ROM chip legs are plated with something bad that tarnishes black and eventually rot away. I would try backing out the ROM chips just slightly and then push back down in the socket to get some wiping action with the chip socket. Look to see if any legs that are broken when you back out the chip. Those fairchild PIA chips often have the chip leg rot too, but they dont look as bad as the ROMs do in your picture.
Other not evasive stuff to try is new PIA and CPU if you have any on hand or could borrow from a different PCB.
