ALSO - Be sure you read the voltage on that red + wire when you try to jump it like you did before. If you got 12V, then set the meter down, and tried to jump it, the battery can go to 1 or 2 volts if it is bad, then recover to near 12V under no load. You have to monitor the voltage WHILE you are trying to start it.
sounds like a bad connection at the starter or a bad starter. Put your volt meter probes between the 12V+ at the starter, and chassis ground, then turn the key. Does it show 12V? If yes try it again with the postive (red probe) on the starter case and the negative (black) probe on the chassis ground. It should not read voltage. This would mean that the starter is grounded ok, and that it is getting 12V ok too. But if the starter case shows 12V (rare) it would mean a bad ground between the starter and chassis.
If you get a good ground on the starter, and a solid 12V at the starter, then it sounds like a bad starter. Do try to pull it thru by hand to be sure the engine is not frozen stiff or hydro locked.