No signal from video card?

I just bought a GeForce 210 to replace a functional 9800GT with a broken fan. After installing the 210, I get no signal to my monitor. So, because I decide on uninstalling the old drivers might solve my problem, I put the old card back in. Now that card wont give a signal. The GALAXY tech support guys told me that I might have confused the motherboard or somehow messed up a setting. So, they tell me to refresh the CMOS. After following the manufacturers instructions to refresh the CMOS, I'm still not getting any signal from wither of the cards. Please help me fix this. There is no onboard video so I have to use a card. It cant be the power supply, like one of the techies suggested, because the 9800GT is a more powerful card, and if it worked with that it should work easily with the 210.