PC Boots to black login screen, help me!!

Ok, here's the deal. I got a new gpu and psu, but the psu was garbage, so I'm gonna have to use my old gpu and psu until I get a new power supply. So I uninstalled all of the new gpu's drivers, put in the old gpu and psu and re installed the old amd catalyst controller and drivers. I then restarted my pc to make sure everything was okay. However, when the computer restarted, when it got to the log in page right before windows, the screen is black. I can see the mouse cursor, and when I move it, it shows the blue circle next to it to signify that it's working on loading or whatever. However, after a few seconds, for some reason the cursor restarts in the middle of the screen, and does the same thing.

I'm using windows 8.1 btw. When I installed the new gou and power supply, I had to enable legacy support in the bios, and disable secureboot. Everytime I loaded it up with the new gpu and cpu, it was fine, although it took a bit longer to boot up to the log in screen.

Now that Ive gotten this black screen thing, I've restarted the computer with the power switch and switched legacy and secureboot on and off. No difference. Please help me if you can.