Strange problem with new card

[Sidneylopsides]

I just got a Powercolor HD4850 1GB from here, upgrading from an X1900XT, I've installed and everyhting seems fine, except for when I try to play a game.
As soon as something 3D starts up the monitor starts to flicker off, like there's a loose connection and it's getting the signal unplugged.
This happens over DVI and VGA, and if I leave it a few minutes, it mostly stops.
Any ideas? Had no issues whatsoever with the X1900 in this machine, nothing else has changed.

 

[Phatzy]

make sure that the games you trying to load is'nt trying to force a resolution that your monitor cant handle.
if not reinstall the drivers again, uninstall driver and clean with driver sweeper in safe mode and restart to reinstall.

 

[Sidneylopsides]

Checked resolutions and refresh rates, made sure my monitor driver was correct too. Even at lower res it does it.
Tried driversweeper, clean install, then again but using 9.5 instead, still the same.
I've tried GTA4, Trackmania, Bioshock and Darwinia, oddly it doesn't affect Darwinia.

 

[HazardO]

What PSU are you using?

 

[Sidneylopsides]

Remember exactly what it is, but it's 500W. Semi fanless, but put it to fan mode. I unplugged anything extra using power in case, so now there is just mobo, one HDD and graphics. DVD is external, mobo and CPU cooled by reserator so no internal fans even.
If it was power, surely it wouldn't improve over time?

Edit: Nesteq Semi-Fanless ASM PSU, 450W, found my order email for it. Not 500w!

 

[Sidneylopsides]

Bump: I spoke to Overclockers, they suggested a PSU problem too, so I got a 650W and put that in, still the same.

 

[[timko]]

Have you tried opening up the CCC and finding the bit to disable VPU recovery? Sounds daft but some google results suggests that it helped some people

 

[Sidneylopsides]

Thanks, I'll try that, didn't spot that when I googled
edit: no luck, can't find the setting!

 

[Mr.Nick]

In the graphics settings on the left, it's right above ATi Overdrive.