While installing a new video card on my pc I have somehow uninstalled or disabled the one that came in my pc. I cannot see anything on my monitor to be able to correct this. Is there any way I can fix this?

It would help to have a bit more information.

What does the indicator light on your monitor do when you boot the computer? turn on and then stays on....makes a pop and starts blinking?...or just continues to blink with no change what-so-ever.

Did you replace the old card? or did you replace the on-board (built in ) video with a video card?

Wour motherboard or computer model? This is so we can look at the board to see if you have what kind of video slots...PCIe.....PCI.....AGP.....

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As a guess...have you removed the new card and gone back to the old one to see if it works that way?

The other option is to remove the new card completely and then reseat it in the socket firmly making sure it is evenly seated...especially after putting in the holding screw or lock down (if tool-less)....Take care as some cards are a bit long and get easily jostled when replacing components

When I turn my computer on the monitor light just comes on and stays on.

The old video card cannot be removed it is connected to the motherboard permanently. The new one will not work without the old one working and it is disabled.

I have an AOL Systemax with Windows 2000.

I have tried both the old and new connections and I get the same thing.
What I need to know is how can I enable the old video card not being able to see anything on my monitor?

I'm not sure I'm totaling following this, but Ill give it a shot.

You have both physically in the machine? On board and the new add on card.
Take out the add on card, plug the monitor back into the onboard connector and see if it works.

If it works, you'll have to do some checking and make sure the add on card is compatible and the resource for it is enable in the system BIOS.