Hi Lina, Have you tried to switch back to the open source driver first and then re-perform the installation process for the non-free driver if need be.
I would: - First undo the installation steps of the proprietary drivers in https://wiki.debian.org/ATIProprietary, don't reboot, - Follow the steps in https://wiki.debian.org/AtiHowTo to get the open source driver running, then reboot, - Re-apply https://wiki.debian.org/ATIProprietary, then reboot. I have a laptop running with an Radeon HD8690M and it's perfectly supported in Debian Jessie/Sid with Kernel 3.13.
