Extremely elusive issue.

At this point I'd say just try it, and post back if things don't change in a few days. I think the real problem was 24/7 running combined with dual antivirus.

Let's see if VEW can give us a clue as to what's causing the freeze-up.

Download VEW by Vino Rosso http://images.malwareremoval.com/vino/VEW.exe
and save it to your desktop

Double click it to start it Note: If running Windows Vista or Windows 7 you will need to right click the file and select Run as administrator and click Continue or Allow at the User Account Control Prompt.
Click the check boxes next to Application and System located under Select log to query on the upper left
Under Select type to list on the right click the boxes next to Error and Warning Note: If running Windows Vista or Windows 7 also click the box next to Critical (not XP).
Under Number or date of events select Number of events and type 20 in the box next to 1 to 20 and click Run
Once it finishes it will display a log file in notepad
Please copy and paste its entire contents into your next reply