Even if a memory stick IS seated properly, the contacts can be problematic, which is why I always hit that edge with a good eraser before reinstalling. The contacts on these things are usually made of steel and/or may have a microscopic splash of gold alloy. Both will oxidize over time. A fresh eraser--one that's not dry or brittle--is soft enough to be safe, yet abrasive enough to brighten the contacts and remove said oxidation.

I returned an Apple Mac G5 to a buddy about three weeks ago that had similar issues. His local authorized Apple repair outfit claimed that the motherboard was hosed and only $900 could get him out of his jam (his Mac made the "bong" startup sound, but otherwise wouldn't boot). The last two DIMMs that I cleaned had dark elipses on the contact area...probably where someone had touched it with their fingers. Brightened those babies up, stuck 'em in and presto, OSX booted.

"Press play and record at the same time" -- Tim Alberstein