iMac mid 2011, gray screen of death!

Hi all! (sorry my spelling Im danish)

I have a iMac mid 2011, 2TB HD, 16GB Ram and an Video Card AMD Radeon HD 6970M 2GB. My problem is the gray screen of death! After boot, i see the Apple logo and the progress bar. When the progress bar stops, the screen goes gray and stops loading. I have tryed the following.

1. Reset SMC og PRAM
2. Start in single user mode, and fsck -fy
3. Internet boot form Apple Hardware Test - No errors at all!
4. Tryed to start i SAFE mode, I see the logo and the progress bar, but it ends with the gray screen of death
5. Tryed to start with only the orginal RAM
6. Tryed to start without anny perihperal eqiptment (keyboard, mouse ect.)
7. Tryed to start in recovery mode and from an USB stik and an install DVD, I see the logo and the progress bar, but it ends with the gray screen of death
8. Tryed to do an internet restotre from Apple, I see the logo and the progress bar, but it ends with the gray screen of death
9. Started the iMac in disk target mode, and got acces from another iMac. Ran Disk Utilities and First Aid, still on go!
10. Started the iMac in disk target mode and made an complet HDD wipe! Made tree new partitions and an clean install from the other iMac. And after this, the probleme iMac cant still start up!
11. I can boot from the probleme iMac's HDD (in diks target mode) via the other iMac, so I guess that the disk in the probleme iMac is in working order
12. I also guess that the screen (video card) on the probleme iMacis in working order due to the fact, that I can see the Apple start logo and the progressbar. As well as the Apple Hardware Test ran via the intrenet (no video error)

Anny surgestions on what to do? Is my iMac dead?

The very best regards Dan