Also, when does it tend to freeze? Is it consistently at one point, like at startup or in the middle of loading programs? Or is it basically random? That could go a long way toward diagnosing the problem.
I'm also interested to know what you've done to test the RAM so far (because as other have said, it IS usually a leading cause of freezing), and whether you installed any new software recently. And what are your system specs? Right now, the only piece of evidence is that the machine was powered off for a long time, which doesn't really rule anything out by itself.