Why won't my 1985 Lincoln Town Car start up?

[igotpotatoes]

I bought a used 1985 Lincoln Town Car and without a jump it won't start. I took it into Shucks Auto Supply and they tested both the battery and alternator. Both were good. They said it might be the starter. I was wondering if it was a bad relay. Car starts up with a jump and drives good but as soon as I turn it off it won't turn over again. Anyone have any ideas of what is wrong and how to fix it? Thanks!