First off, an overall description of the base problem: Upon running my computer with certain video cards/GPUs, my monitor no longer displays any picture after around 5 minutes typically.
Okay, so I originally have an ATI Radeon 6900 series GPU and it worked perfectly fine for quite a long time. I then got a new monitor, a 27 inch LG monitor (not sure the exact model, can get if anyone thinks it'll help) and the card still worked perfectly fine with it for about 2 weeks. Suddenly while using my computer, the issue happened the first time, the screen just went black. I thought something might have overheated or something. After some more troubleshooting and having it happen a few more times, I realized that audio still plays from my computer while the screen is black and I can still press buttons to perform actions during games and such. As such, I'm saying it's simply me losing output to the monitor or something of the sort.
I then tried my old ATI 5700 series GPU which worked just fine with zero issues. I figured that my 6900 series GPU must have have died in some way and wanted to upgrade a little anyways, so I ordered a NVIDIA GTX 670. I received it, then proceeded to install it and all, only to end up having the same no-monitor-display-after-short-time issue again. I again put my 5700 series back in and things worked fine.
My power supply should be well enough (Antec EarthWatts 650), but it's all I can figure to be the issue...
Wanted to see what other people's opinions/thoughts were before I went and ordered a new power supply though. Can supply exact GPU models and such if needed.
Other specs: AMD FX 8320 8 core 3.5GHz, 8GB RAM
Thanks for any help!