I am trying to install an x1650 pro video card in my sons dell dimension 4600. I am not a techy, but I can usually follow instructions and get the job done.

I read in another forum that this AGP card is compatible with this computer.
I have actually tried two different vid cards and both of them are not recognized by the monitor. I confirmed compatibility of the other card awhile back but never installed it.

This is the really weird thing, while the video card is in the slot, the monitor will not work with the onboard video either. I put it back in the regular spot and nothing. This happens with both video cards, the monitor stays black. Take the card out, put the monitor in the regular port and it works fine.
BTW The AGP is 8X and so is the card.
Now, I have tried to disable the onboard video in the setup, but it only lets me pick "onboard" or "auto" for video and won't let me disable. I can disable in the device manager, but not sure I am actually disabling the correct thing.

I previously had a 9800 pro video card in this computer. At that time I was able to disable the onboard video in the setup/bios. I had to take it out because although it worked, it got crappy after a short time due to the too small power supply. I couldn't figure out how to change that in the dell so I sold the card on Ebay.

Now I realize I have to upgrade the power supply and I have one that will work, and I have figured out how to do it, but I don't feel like doing that until I get the video card installed.

For the life of me, I cannot figure out what would be causing this problem. I have had help from people who know alot more than me and they can't figure it out. BTW, The fan is running on the card, but the monitor (and another, I tried two just in case) doesn't recognize the card at all.

I am sorry for the lengthy post, but figured you would need info for this...Any idea's what would cause this???

Disabeling in "Device Manager" isn't gonna help much if any. I'd wait until you get some reasonable service before you go there. After you get the drivers, etc. installed, you may not need to. If the BIOS isn't picking up the new GA you'll have no hope of going further.
The onboard adapter MAY have a jumper setting which you can use to disable it if the BIOS itself gets balky.

a similar thing happened to me not long ago i upgraded from a geforce 7 to a geforce 8 and when i put the new card in and booted up the pc i could hear windows starting up but the screen was blank.
i have to say my pc is custom built and i was using vista 64bit so it might be completely different for you.

how i solved this was to simply boot windows with the old recognised card installed and log on, then i went into system device manager and uninstall the graphics card drivers for that card.

note: now i dont know if this will be a good thing for you to do and whether it is irreversable but if you have nothing left to try it might be the way forward

anyway once i uninstalled the drivers windows wanted to reboot but what i did was to shut down instead.

then i took the old card out, installed the new one and rebooted windows, which then found the card and installed windows basic drivers which i promptly over installed with the latest nvidia drivers

job done!

searching online it seems that if you go into the bios and set on board graphics to auto then when you install the new card it should auto disable the onboard

silly to say it but just make sure that change in the bios before you exit and make sure you plug the monitor into the new card.