So I just bought a new graphics card (Nvidia Geforce gt 630) and installed it, but I'm not getting any video signal. So I took it out and put the old card (I believe radeon 5450 hd or something) back in. The old card is not giving any video display now either. I also cannot use onboard graphics because I believe the onboard graphics have never worked. Weird, I know. Please help, this is my first time I've ever messed with the insides and I'm terrified that I've destroyed my whole pc.