Need Help - At A Loss

After building a PC for a friends son last week, everything was fine for about five days when suddenly the display turned off and he got a "sync out of range" error. After rebooting, you see the POST screen and RAM count etc, then the screen cuts off and "sync out of range" appears again.

Phenom II 1090T Black Edition @ stock 3.2Ghz
Biostar mobo with 4 PCi-ex slots
8GB (2x4) Crucial DDR3 1600
Corsair 700W Modular
XFX 2GB 7850

First thing I did was check BIOS, nothing wrong there. So I flashed the bios to the latest version which fixes errors reading drives above 3TB. Still got Sync Out Of Range error after POST. :cry

The PC works FINE with his old nVidia 8800GT card. Put the 7850 back in, and Sync error. I've cleaned all AMD drivers and reinstalled them. Reformatted his HD and fresh install of Windows 7 + all drivers, still didn't work. Tried running through HDMI, DVI, Displayport ... still nothing. I also tried a friends 6870 and guess what? SAME thing happens with the 6870, Sync error after POST. :confused

Has ANYONE seen this before? What can I do now? :major

 

Can you post the model of the biostar motherboard please. Check the manual to be sure the card is in the right PCI-E slot, try a different slot. Triple check all motherboard power connectors are connected.

I doubt it's a driver problem as the video driver is only loaded after the windows logo.

Will it start in safe mode? Start tapping F8 during the post screen.

Have you tried a different monitor? With speakers connected let windows load, when the monitor turns off does the windows loading music play?

 

Thanks for the reply :cool

The motherboard model is Biostar AM3 TA890FXE.
I tried the GFX card in the first 3 Pci-ex slots, does the same thing every time. All motherboard power connectors are installed (the main 22pin board power and both 4-pin powers are in tight). I agree that it's probably not a driver issue, but I tried the re-install anyway just because I was running out of ideas by that point.

I didn't try safe mode because by the time POST ends we already lose the video signal. Tried 3 screens - two monitors and a 32" Television, and the same thing happens on each.

The only thing I haven't tried is leaving the PC for 2-3 minutes or so and seeing if we actually get into windows. I will do that when I get to the PC again.