Is there any other sign of life? Any beep codes?
Try re-seating the video card. Sometimes the spring contacts don't behave. I had that happen before-- but I did hear a beep code. Completely power off the system first (not just ATX soft off, flip the power switch or unplug the power cable) before re-seating.
Do you have a good power supply? Were you doing any overclocking of the AGP slot?