Computer freezes when idling

[MadEmperor]

I just built a new computer about a month ago, and I've had an issue where my main monitor goes black and the computer freezes. Specs:

i5 quad core 750
4GB Ram DD3 1600
750w 80+ Bronze PSU
Radeon 5870 (previously Radeon 5850)
Radeon 4350 secondary GPU
Intel X25 SSD
ASRock P55 Extreme Mobo
Windows 7 x64 pro ed

The freezing happens about once every other day when I'm not gaming. I should note that it never happens when I game, which I do more then site idle just browsing firefox. It has happened when I use just firefox and when I was writing a term paper (thankfully I backed up prior)

When it freezes the main screen goes black, the 2 remaining screens still have a picture but I can not move the mouse or anything else

I noticed some other small issues:
If I turned on the Radeon built in OClock even at stock clockrates it would freeze
Sims 2 would not render sims correctly

I decided to buy a new video card, at worse it was an excuse to upgrade. The new Radeon 5870 does NOT pixelize and freeze when I use the Overclocking utility, so that's a plus. (I did a complete driver uninstall CCcleaner the works and got the newest drivers)

The freezing and sims2 problem is still there (I figure Sims2 is just a driver issue that will hopefully be fixed in the future)

Thoughts on what could be the cause of these Freezes?

 

[TJCS]

Seems like your PC is going into power saving mode and somehow getting stuck there. I think it is wise to turn off power-saving options in your computer, since you don't need to save battery power.

You can try these two things:

1. Start>Power Options>Choose "High Performance" (default is balanced)

Go inside plan settings and disable all auto power saving options (turn off disk options, sleep, and etc. to never).
​

2. Do you have "Enhaced Halt State" or "C1E" (can usually be found in advance cpu options) enabled in bios? You can try turning disabling it and see if you still experience the freezes. Detailed info on Enhanced Halt State.

 

[SolMiester]

I'm a little confused, you are running 2 graphics cards?, surely not crossfire?...doesnt the 5870 have 3 outputs?....why the 2nd card....

PC freeze is usually API hardware drivers or RAM issues!