You found a pawn shop that still has old Macs? Man I wished I lived where you live.

I do know the music store in my town has an old PowerPC Mac (similar in design to what you have), but never did see (or recall) the exact model. It was in the back office though and I don't think they are going to sell it.

But yeah, check the RAM and the other removable hardware to try and find out the issue. But if all else fails it may need to have the capacitors replaced.