GeForce video card and Asus Mobo problem.

Here's my situation - I recently upgraded my main PC's video card to a BFG 6800 GS (Putting off PCI-E for as long as I can). Because of this, I figured I'd swap my old video card into my secondary PC. The old card is a Gainward GeForce FX 5900XT AGP card. The board I tried to install it on is an Asus A7N8X-X which previously had a GeForce 3 Ti200 card. Anyway, I installed the 5900XT card properly on the Asus A7n8X-X board, hooked up a power connector to it, but when I try to boot the machine, there is no video display whatsoever. My monitor stays in standby and apparently never gets a video signal. If I put the 5900XT card back in my primary PC it works fine. If i put the GeForce 3 back on the Asus board, everything is fine.

Any idea what the problem is? According to Asus' website the board supports 8x AGP. A power supply issue wouldn't prevent the monitor from getting a signal right? I've accidentally booted a PC when I forgot to plug a power connector to the card, and it got into Windows fine, subsequently reporting insufficient power to the card. I can't even get the Asus machine to post with the 5900XT (And I've verified the 5900XT works in two other machines). In fact, it's in my girlfriend's PC as I'm typing this.

This is the first time I've been completely stumped by a PC problem and it's driving me nuts.

perhaps it dosent have enoguh juice ? "watts", how many watts is the psu ?

It's an Enlight 300 watt PSU that's lasted many years. I believe it can do 18a on the 12v. That should be enough to power up a 5900 card shouldn't it? I'm going to swap it with a Fortron 550 watt to be sure, but I'm not very confident that is the problem. I just flashed the Asus board to the latest BIOS, I'll see if that fixes it first.

Uninstall the previous video drivers before installing the new card. That way it starts on default windows drivers. If you are getting no picture at all (can't even see POST) then it is more than likely your PSU is not strong enough. 300w is very weak.