When you put the switch back to the default bios does the system boot? How do you know your flash was successful if you can not boot with the flashed bios? Please tell exactly in detail what you did and with what software. I have flashed quit a few and it is hard to know what may be your issue without more detail.
The problem is that after I burn the BIOS of HD 6970, I try to restart my computer to apply the changes, and it simply doesn't load. Does it mean the burning did not succeed?
In order for the computer to start properly, I need to move the switch back and only then it works. In other words, my card with BIOS OF HD 6970 makes my computer fail to turn on, but only with original BIOS of HD 6950.
Ok so you can run normally with the stock bios. That is good as it means you did not brick the card on the hardware level. If you used a 6970 bios for your replacement bios in position 2, you may have bricked the second bios. A 6970 bios is not what you needed. You needed to copy the existing bios and then mod the copy to activate the shadders and then flash the modded 6950 bios back in. Your flash attempt failed..yes. And you may have bricked the #2 bios. Your only path at this point is to try to restore the original #2 bios. You did make a copy before flashing right? If it flashes back and you can start the system with either bios, then you may be able to unlock the shadders on a copy of the #2 bios. If you have not saved copy then you can make a copy of the #1 bios and flash it back to the #2 bios. Then try to unlock the shadders on that copy of the new #2 bios. If that works then you can try to use the modded #1 bios to flash into the #2 bios position. Be aware that in recent production versions of the card (even the ones with a switch) the shadders are physically disconnected on the chip. No amount of bios mods will enable them. I do not intend to insult but from your reply I would say you do not know what you are doing and would be best served by using the card as supplied by the manufacturer. You have already voided the warranty so use care in what you do. GL