Strange video issue

[Bambi72]

I have an BFG 9800GTX card which works perfectly, however if I shut down or reboot the PC, when windows restarts and gets past the login screen I lose the video signal to a black screen after about 10-15 seconds. The gfx cards fan is running nice and fast as I can hear it so I doubt its that overheating, when windows boots normally it hits about 85 deg C at 100% usage running CUDA processing apps. The PC appers to be responding still ( I can toggle num lock caps lock etc which is always a good test for a hung system with no display) just no video signal.

If I switch off the power at the PSU switch when the computer is off, and wait for the power LED on the mobo to turn off (about 3-4 seconds) then reboot the system starts up perfectly withno problems until I reboot.

Anyone had anything similar to this before?

I have an Asus M3N-HD mobo, AMD Phenom 9550 quad core cpu, 4 GB RAM running Vista 32bit with all the latest patches drivers etc.

 

[cube_]

I can't say i've ever run into such an issue. It seems to me that your motherboard is selectively switching to it's integrated video card (GeForce 8 series) and you get a blank screen because no monitor is connected to it. I'm almost sure that's the reason.

What startup items do you see? Is there anything like a GeForce 8 driver loaded up? You could try disabling the GeForce 8 display from Device Manager.

 

[Bambi72]

I have the onboard video disabled in my BIOS, so I don't think it is that.
Interestingly I changed the Power button ACPI settings in the bios from S1 &S3 to just S1 and today I didn't have to do a cold boot to get the box working. I'll update if this seems to be the root of the problem.
The strange thing is that if I leave the PC at the windows login screen it will sit there happily for hours, its just when I log into Windows that I lose the display. Only had this problem recently as the PC used to stay on 24/7.