Let's not make trouble; ATI is a opensource driver, fglrx (AMD Catalyst) is a proprietary driver; There is no ATI Catalyst.
I am running LM14, Cinnamon 64bit, with kernel 3.5.0-17-generic (default), with AMD Catalyst 13.12 working fine (see my signature)
Try to uninstall fglrx (AMD Catalyst, if you installed it)
Update your kernel (If you need it)
Update your system
Reinstall AMD Catalyst
Never upgrade the kernel with proprietary driver installed; before you uninstall this.
LM16 Cinnamon (PC); LM14 Cinnamon with AMD Catalyst (notebook)
HP Pavilion g4-1316br, AMD Quad Core, 1,5 GHz, Radeon 6520G/7450M,
Linuxcounter Registered User #506065 (2008)