G4 Freezing up on me...

[slomo86]

OK I am running a G4 450mhz with 1.5 gigs of ram, and 2 100 gig hard drives and one 20 gig hard drive, and I am running Tiger with all the updates. So if I leave my system on all day at about at 1 or 2 in the morning my computer will just freeze up on me after a few mins of not using it. Usually it acts like its going to goto the screen saver but it just goes black and I can't do nothing just move the mouse, or it will just freeze as is and can't move the mouse. If i have iTunes running it will keep playing the music. Then I will restart it and it might do it again or Safari will start acting up, it will open and as soon as the homepage loads safari will close and will say that it unexpectedly quit and asks if I would like to restart safari I click restart and does the same thing over and its just a circle untill I restart the computer again. That seems to clear things up. The only thing I have really done is cloned the system hard drive (the 20gig) over to one of the 100 gig hard drives and running off that. But it was still doing it before that, just not as offten. Now its every other night or so. Anyone got an idea of what it could be and how to fix it???