|"I have too important data in C and can't risk to install a fresh copy of 7"|
Why would you need to re-install Windows to fix a driver problem? And why is it that you can't uninstall the ATI driver from Safe Mode - what happens when you try? It should uninstall. If it doesn't, it's possible that the driver is corrupted or didn't install correctly. Since you said it's the latest driver, I'm guessing that you didn't use the drivers disk that came with the card, so you must have downloaded the driver from the AMD/ATI website?
You didn't say so in your explanation, but I assume after you removed the nvidia drivers & shutdown, you physically removed the nvidia card then installed the ATI card in it's place?