This is my lemon PB G4 that the girlfriend has been using after her PC died: It was acting up like this for a while, but the problem eventually went away after being turned off and allowed to fully cool. The machine started having the problem full time tonight. This laptop has been in and out of Apple's repair department and Apple stores the entire time I've owned it. The HD has been wiped just recently as the Apple Store's way of "solving" the issues it was having, namely unexplained freezes and fan noise. It's also on it's 2nd HD after the first one died without warning. Any ideas what's causing this? Is it reasonably fixable?