Ok an update to my Error is coming up.
After some digging in logs i ended up with the following error:
/usr/lib/X: symbol lookup error:
/usr/lib/xorg/modules/drivers/fglrx_drv.so: undefined symbol:
(Typyng it by hand from my MacBook)
This happened after i used sudo apt-get upgrade command to update my desktop. Linux Mint 14 Cinnamon Edition. 64 Bit.
So, i fould a solution saying that i have to reinstall my Radeon drivers, but im not sure how to do it by using live USB?