I fixed one of these Greyhound Electronics games for a guy last year. It looked like this:
http://flyers.arcade-museum.com/?page=flyer&db=videodb&id=4271&image=4
If yours is similar, you might find...
There's a 22/44 edge connector on the PCB. Remove it. It's only used for inputs (buttons, button lights, coin, lockout, and test mode, IIRC). Power and video are on seperate connectors, so it should boot up and show attract mode (but not start a game).
You might try playing it like this... jumper lines to GND (A & 1 on the edge connector). For example, coin is 10 (solder side), the top row of 5 buttons are 15-19 (also solder side), deal cancel & stand are 20, 21 & 22. The last button (Play / Raise?) is C, on the parts side.
If you determine it is a board problem, first take a good close for broken traces, esp on the end of the PCB near the edge connector. There are two 8255 interface-I/O chips on there that go between the buttons and the CPU.
Hopefully you'll determine that the board is fine, and instead you've got connector issues (either the split pins in the edge conn., or one of the molex connectors between it and the housing, or at the quick-disconnects to the buttons).