Dell Computer problem. Need Help ASAP

Hello,
I got a really bad problem with my computer. The monitor, and CPU are both Dell. The monitor keeps showing a orange light after 5 seconds of a green light. I was confused, switched the monitor, with an older one, and the old monitor's green light kept flashing. I figured that the probleme as with the video card, but then how do I change it? The monitor shows nothing. Please help ASAP!