System hangs

I have a Dell Dimenstions 4800 P4 2.4 gig PC. I am runniung XP home w/ SP2. I have had this machine for a little over a year now. The problem that I am having is this: The computer seems to hang every now and then. Usually this will happen when I am not using it after it turns on the screen saver. But every now and then it will happen when the PC is in use.

I had this same exact problem with the PC that I replaced with this one. That machine was a P2 350 running xp home w/o SP2. The first thing that I thought that it could be was my belkin USB hub that I had with the old machine, because everytime it hung up the lights on the hub would all be out. So I disconnected the hub and ran everything directly into the dell except for my flash card reader and my Axim PC link cable. After a week the without the hub the problem would still happen. So I started disconnecting hardware from the usb ports that I had when I had the old machine. This included just an external HD and a printer.

I have noticed that it happens a lot less now with out the external HD attached, but it still happens every now and then. I don'w know if this is a hardware or a software conflict so I will post this in both forums.

Any help would be greatly appreciated.

Thanks