....the motherboard. Try switching in a known good monitor and see if that makes a difference. If not, then you swap in known good cabling. After that, it can only be the the motherboard which is failing to work as designed.
Hope this helps.
I've recently built a new computer from scratch and it was working fine until it started freezing randomly. It started after about a month of using the computer. It's not the video card because I've been through 3 of them and it still does the same thing. I tested the ram as well and that was fine Any ideas? Here is what it looks like this http://i1381.photobucket.com/albums/ah205/gokusuper57/0105161818c_zps4afklmjt.jpg