Windows ME locks up Overnight

Hello,
I am using Windows ME on a Novell 5 Network. It seems that overnight, if I just leave me computer on, it locks up. The next morning when I come in my mouse is locked up, (basically the whole computer is locked up). Is there any reason that this is happening? I don’t have any tasks running (such as a Defragment) that would cause it to lock up. I am not using a screensaver, or anything like that to cause it to lock up. It just seems ridiculous that it locks up every night. HELP… !!! 🙂