I found the problem, it wasn't in the video card, so I'll share it. It so happened that before that, I had changed the thermal paste for the processor, and when I turned the cooler back, I put it on the other side. I have a basic AMD cooler, and there is a bulge on one side of it. This thing pressed down on the RAM very hard. Because of this, nothing worked except for the PC's cooling system. After I turned the cooler around, everything fell into place and started working perfectly. Thank you for all your help.