gpu display

I have been struggling with a problem occurring on my computer recently. Often i have trouble booting my pc up, I turn it on. (Fans spinning everything working RGB on etc.) But no display and signal on my monitor. After rebooting for a couple of times and re-plugging my GPU power and display...

I had to move recently, and the owner of new apartment generously allowed me to use his old GPU which was just laying around. It was Radeon HD 7770, but since my GPU at the moment was even older (Nvidia GTS 450) I decided to give it a try. Everything seemed to work, and for 2,5 - 3 weeks I...