powerbook 3400c-ram or computer issue?

hi everyone, a while back i bought a powerbook 3400c for cheap on craigslist. great machine but when i looked at the info i saw it had only 16 megs of ram. i checked ebay to upgrade and i almost fainted at the prices for 'vintage' ram. so found a 64mg ram card (ended up being the wrong kind-doh) and opened up the mac. lo and behold there was a 128 mg card already installed-but the powerbook doesn't recognize it. i tried removing and reseating it- no go. i know the obvious solution would be to get another ram card and test that but given the ram prices and the fact that i don't know if it's a computer or ram card issue, is there something i could try to test/solve/workaround before i shell out the big bucks? thanks in advance