I recently bought a GeForce 6200 256MB TV-Out/DVI 8xAGP - OEM for my PC.
Upon reading the instructions and carrying them out to the tee, the following happens. The card is installed, the blue monitor lead is plugged into the graphics port, the pc boots up and the VDU comes on, displaying the boot sequence. The screen then goes black.
I currently run a IMEDIA 1401 PB13108601. The MOBO is a Gigabyte GA-8SIMLNF7 running a Celeron D 330 2.66Mhz processor. The AGP bus is SiS651 8x running integrated 64MB graphics with no actual video card. I currently have 512MB of RAM.
I have been into the BIOS to ensure that the AGP port is there and selected. I have also knocked up my graphics ram from 128MB to 256MB.
I went into the BIOS and also add/remove programs to disable the onboard graphics and to delete the existing drivers, but both of these are not present, so i'm unable to do this.
I then went into Device Manager and disabled the display adapter SiS651C
I have slotted the card correctly into the AGP port and ensured that the white clip is fully engaged. But when i boot the PC up the monitor still is black.
I've had the same exact problem twice with old AGP machines, both when installing a new card for the first time to replace the onboard graphics.
Of all the things I tried, what finally fixed it was taking out the CPU and reseating it. That apparently gave the motherboard a kick in the a** so that it thought it was a new system build and identified the "new" components, including the graphics card. Of course, who the hell knows if that'll work with a different motherboard and a different card -- or whether it was peculiar to my machines, both of which used the same model motherboard.
A less drastic but similar idea might be removing the battery to do a CMOS reset and see if the board will identify the new card while starting from scratch.
Again, these are not "by the book" methods for fixing a video problem, and not what I'd normally recommend trying first. Only reason I mention it is because you're having a remarkably similar problem to mine, and it sounds like you've already tried the by-the-book approach and it hasn't done anything.