Alright so I got my new power supply and graphics card and after a while of putting a huge graphics card and psu in my minitower I tried everything and it didnt work. I turned it on and after about 3 mins the screen went blank and said no video signal, but everything else was still running fine. I restart and only got about 1 min. And then 45 seconds. Then I let it sit for half hour nad got 2 mins out of it. SO i put in my old graphics and make sure i fully uninstall it, and i did. Try it again, same thing. So idk. My psu obviously works because I'm using my old graphics card atm. And when I took out the new one it was VERy hot. I had to let it cool for little before i could remove it. Im guessing that the graphics card gets too hot and just shuts down? I would like to try as many solutions at once so I dont have to keep taking it in and out just to test one little thing. Any help/tips is helpful.

psu= PC Power & Cooling S75QB 750W
grpahics card = VisionTek 900244 Radeon HD 4870