often means the CPU isn't working. I know many will get into the whole logic probing thing, but I'll concentrate on mechanical matters first (as I suppose my name implies).
the CMOS battery that Pole Position used is mounted in direct proximity to the main CPU. when that battery leaks, it winds up gobbling that section of the board and in my estimation will leak into the CPU socket. once that happens, a number of connections wind up broken, and the CPU can't talk to the rest of the board like it's supposed to.
the battery is in the bottom middle portion of the board -- if the battery is still there, chop it off. if it isn't, inspect for any battery leakage corrosion. it'll probably be white or green, though I think that was a rechargeable nicad or something, I don't know what that means then. I just know they're bad, and the usual method of white vinegar doesn't work like it does with alkaline.
post pictures if you can. it's the Z80 chip by the battery.