iBook G4 not recognizing RAM

Hi,

I pulled a 256mb stick out of the girlfriend's dead PC laptop and it fits in my 14" iBook G4 and when I originally put it in, "About this Mac" said I had 768mb, meaning it recognized the new RAM, now its about three weeks later and "About this Mac" says its 512mb again.

So, I pulled the RAM out, put it back in, it recognized it for about a day and now its back to saying 512mb.

I know when you buy RAM new, it comes with a CD(usually) to scan your computer, so is that the problem and if so, is there a download of the software online?

If not, then any advice on what to do or what the problem might be would be greatly appreciated.

Thanks for your time,
Nathan

Edit: Im running 10.4.8, if that helps.

Thanks,

Yeah, crucial says its pc2700 and the stick I put in is pc2100.

Oh well.

Thanks for your help,
Nathan