my old system cannot take the New Card and the other way around. My systems are about 5/6 years apart...
Is this a completely new build? If so, go through this check list
Do your fans, motherboard, HDD etc power on when you start the PC, is there a speaker connected to your motherboard so you can hear possible beep codes?
Try reseating the video card, and make sure the power cable is securely connected.