Monitor no longer working

Does your card have a fan? If so, make sure it is going; it may be the power cable just got slightly disconnected.
Try completely removing, blowing dust off, and reinserting the video card carefully and fully. Never hurts to make sure everything's tight and connected.
Also, look for signs of a transistor or something on the surface of the card that you may have broken or bent when you bumped it.

Hope you get it working again.

First thing you should do is unplug the monitor from the graphics card, plug it into the motherboard's built-in video port, and see if you get a picture that way. When a slot is emptied and then something is re-inserted, there's a chance that your machine assumed it was "new hardware" that it didn't have a driver for, and reverted to its onboard graphics adapter. Especially if you ever had the machine powered on without the card in. I don't know the sequence of events leading up to your problem, but it's worth checking out.

If you get any signal that way, you may be able to get the card working again simply by disabling the motherboard's onboard graphics (there's usually an option in the BIOS). You may also try re-installing the drivers for your graphics card.

Just curious, but how "slightly" did you bump it? Usually the graphics card is screwed down to the case at one end, which would take a pretty serious jolt to overcome. My first instinct would be to check that something was bent, but I wasn't there.

You DO get signal long enough to see the initial boot information come up using at least one of the ports, right? If so, go into the BIOS and switch your onboard graphics to enabled, then try to get into Windows from there.

If you get nothing at all from the card and nothing at all from the onboard port, first try removing the AGP card and plugging the monitor into the onboard port to see if you'll get signal that way. If the computer sees nothing in the AGP slot, you may get lucky and it'll automatically re-enable onbard graphics. If not, you can try removing the CMOS battery from your motherboard. Let it sit for 10-15 minutes (unplugged from the wall as well, obviously) and it will reset the BIOS to default factory settings, which usually means onboard device is enabled. You'll probably want to have the AGP card removed for this part also.

If you can get into Windows that way, put the graphics card back in, reboot, and then look in the Device Manager to see if your computer is detecting the card at all. If it is detecting the card correctly, it should be under "Display Adapters"; if not, it could be listed in a number of places as an "Unknown Device" or "Unknown VGA Device," in which case you can try reinstalling the video card's drivers from there. (while you're in the Device Manager, I feel I should point out that under NO circumstances should you disable a device called "Vgasave," which is Windows' emergency backup graphics driver if neither onboard or a working card is detected. Disable that and you are in for a world of pain).

If you still can't get it to work after all this, next step would be to try a different graphics card in the slot ... if you can get that to work but not the old one, it likely means the old one is dead.

Out of curiosity, what video card ARE you using?