I had windows melinum and had similar problems. I formated several times until I was told the OS was causing the problem.
Went to XP and it was fine.
Have you tried a reformat?
Haven't tried that yet. My dad got a copy of xp, but I can't get into the system to even use it. I've taken out each stick of ram to start it up....nothing. Used one HD to start it up(the one with the os on it)....nothing. I've used the other HD by itself as well......nothing. It hasn't actually started at all lately. everything seems to be in order...I took it apart and checked for any damage, seems fine....all fans run. it just refuses to boot at all now. Just black screen. I think that either A the MB is in fact bad or B the processor is shot. could be both for all I know. Is there a way to check that before actually buying new parts or am I going to have to risk it and buy a new one lol. I seriously appreciate all the help though guys. Just trying to narrow down my options. The last time it was functioning at all was 2 days ago. No matter what I tried or how long I've waited I can't get it to boot up.

I'm using a laptop right now.