What OS is it running? I would recommend pulling the RAM upgrade out of the computer (if there is one, it's under the keyboard and below a little metal shield secured by 4 Philips screws). Remove the stick and run it like that. If the problem doesn't happen again, the SODIMM chip is bad. If it continues, the soldered RAM is bad

I had this happened to me on a 466MHz graphite iBook. I was so mad since it was one of the SE models, but the seller took it back and all was well.