Hello Motor
Well I am talking about case fans.
Most comps have atleast 2 fans attached to the case.
One would be up front and another would be at the back. the one up front sucks in the air (Hopefully cooler air) and the one at the back sucks the hot air out. But if the room temp is hotter then the air in the case then it is doing no good no matter what. Your comp will not cool down.
I myself have have 7 case fans 4 suck in cooler air 3 suck out the hotter air plue there is a fan on the power supply and the heat sink and on the V-card.
When you tried the comp again in the morning was the comp left on all night or do you shut it off at night. I ask becuase some people never shut theres down it runs 24/7

In most cases it do's not hurt anything is you have a screensaver and or you set it to go to sleep where it semi shuts down. But for me on real not days like we are having now it is a good idea to shut it down if you are not home and not useing it.
In any case with it locking up and the monitor screen going black it still sounds like to me it is a heat problem. and I would point the problem being that the V-Card is getting hot and that is where it is locking at.
Spicificly when you stated the the both times it happened you are watching a replay, and that puts a little more work on the V-card.
I do not think anything major has went yet since it is still turniong on and running.
Just have to find the bug
I hope this helps
Hitman

I might not be fast, But I am ahead of you.
Ruben Hitman Miranda