I would assume it's a psu problem. If it was a video card issue you should hear beeps and will not boot or BSOD. It also could be pcie problem since reinserting your card makes it work. HD 7750 takes all its power from pcie so it might be the connection. If you can borrow a psu try that first, If it still does the same try a different video card or try putting your hd 7750 to a friends pc.