You need to either try the video card in another computer to see if it works, or get another agp video card that you know works and try it in your motherboard and then get back to us.
There isn't any reason why the agp slot should be disabled. Of course it could be bad but that's why you need to test your parts.
There isn't any reason why the agp slot should be disabled. Of course it could be bad but that's why you need to test your parts.