Most likely your 5101 chip has died or has some corrosion under the socket.
Easiest thing to try next is probably to swap out the this chip.
I think Ken (Skybeaux) had some available for sale, if you don't have a spare on hand.
You can PM him here
http://aussiepinball.com/index.php?action=profile;u=162Edit. Might be worth trying the On/Off trick again now that you have confirmed all battery voltages are present and correct. Just make sure you have the coin door open when you try it.
