The fuse at the center has blown out. (PS14 on V7)
-[reffer to charlie_ps2's fuse charts for versions other than V7]-
This was likley due to a bridge.
I have had this problem before and so did others.
check that PS14 fuse with a multimeter by placing one pin of the mulimeter in one side and other on the other side of the fuse to see if its blow out. If its good check the rest of the fuses and the BA chip.
If the fuse has blow out find the fuse/similar fuse from a broken ps2/psx board.
Vengeance causes one to act blindly through anger, rather than through reason.
V7 PS2 W/Messiah 2 Pro v1.21
XBOX W/Excuter 2 Lite