Windows 7 won't boot on Crossfire R7870

[tehkemo]

Hello Guys, I'm struggling with a problem on my PC, the specs are:

CPU: i5-3570K (default clock atm)
Mobo: AsRock z77 Extreme 6 (UEFI 1.60 - didnt flashed yet)
GPUs: 2x MSI R7870-2GD5T/OC (default clocks)
RAM: Kingston HyperX Genesis Grey 8GB (2x4GB) DDR3 1600 XMP (currently running at 1600MHz)
PSU: Fortron Aurum 750W
Properly cooled case CoolerMaster HAF edition.

PROBLEM:
The problem I'm experincing, is that I can't boot up in Windows 7 with both cards connected to MOBO. After both cards are installed in mobo - system display BIOS post, then just black screen and reboot - and this goes all the time until I shut down.

WHAT I'VE TRIED:
While with one (no matter which one Ill choose), it works fine - I've tested them separately, GPUs are fine - no artefacts, no issues at all.

I've installed fresh Windows 7 x64 - updated to current date (all updates including SP1). Installed 12.11 beta 8 + 12.11 Cap 1 profile.

Also, I got to mention it's for me only possible to instal Windows 7 with one GPU installed in MOBO so I did that way. After installing all latest drivers for Windows 7 x64 from AsRock Website I have installed GPU drivers + App Profile, then restart, to finish the process. Shutdown, installed second GPU and the problem popup. Windows is not bootable anymore even after removing second GPU.

I have also tried to install GPU drivers, restart, then in device manager "Uninstall" 7800 GPU" and shutdown immediately so Windows dont use own drivers for this GPU. After adding second GPU the same result - won't boot.

What's even more shocking - I have installed Windows 8 (with both GPUs installed in mobo) and without any issues I've been playing FarCry 3 on Uplay in Crossfire on ultra details for like 2 hours - no issue at all.



I'd really appreciate any help, clues, links in this problem, because I've really tried to solve this without bothering you guys.

Thank you,

Regards,
Tom

 

[alvine]

update your motherboard's bios, download intel update tool to get the newest drives for your chipset

 

[tehkemo]

Im about to flash BIOS, you suggesting the latest one or better stay with a bit older "solid & community tested" version of BIOS ?

Thanks,
T.

 

[tehkemo]

I've updated to the latest BIOS, also the latest intel chipset + Ive checked all the drivers in system => latest.

Windows is not giving me any BSOD, error msg etc. After BIOS post, black screen with blinking "underscore" in the top left corner and then immediately Windows Starting screen should appear, instead that just REBOOT and BIOS post again...


I've checked EVENT viewer as well, but I'm worried it wont even get chance to save some error or something there, since I've not seen any suspicious errors.

Maybe there's some other log with boot activities that I should check?


Thanks,
T.