Ubuntu 12.04 freezes

Hi everybody!
I upgraded to Ubuntu 12.04 LTS not long time ago.
Everything went smooth with the installation.
Soon after I began to experience freezing of the system.
It mostly happens when I scroll the mouse wheel ,but recently it happened also without obvious reason.
When it happens I have to reboot the system to overcome the problem, but soon after, it freezes up again.
Now I'm writing from windows because it simply impossible to work from Ubuntu.
If someone experienced those problems with Ubuntu 12.04 and has a solution, please let me know.
Thank you in advance,
Nir