Since I've had this Vista machine (since 2008), this is the first time I've ever had this issue. About 85% - 95% of the time, when I leave my computer idle for a few hours and come back, everything is frozen. I can leave for any length of time, and it never unfreezes on its own. Ctrl + Alt + Dlt doesn't even work. The only way I can get out of it is if I unplug the power cord from the back of the machine, then plug it back in, and hit the power button to start it again. Of course at this point, I get the black screen which asks if I want to start Windows normally or go into Safe Mode, etc. It's starting to get old, and I need to find the resolution.

Just so that there is no confusion, I don't have 'Sleep' activated in the O.S. itself, and I never have. The only thing that goes to sleep after about 20 minutes is the monitor itself, which wakes up immediately when either moving the mouse or tapping any key on the keyboard.

Fist thought is that maybe there is a virus causing it. I've done a full system scan with Malwarebytes, and it found nothing. The next step I was going to do along those lines was to perform a full system scan with Nortons, because from my experience, sometimes malware is found between the two full-system scans, when one of the anti-malware/virus programs doesn't catch it. It might not even be related to malware, IDK, so that's why I'm asking for help on the next troubleshooting step. Thanks.