Temporary fix:
Boot into the previous kernel version,
Reenable the fglrx driver from System > Administration > Hardware drivers and reboot again to the previous kernel. In my machine it is 2.6.24-11-generic.
I don't know if this will work if you updated from other ubuntu versions. I was already in hardy.
kernel 2.6.24-12-generic is the problem.
Temporary fix:
Boot into the previous kernel version,
Reenable the fglrx driver from System > Administration > Hardware drivers and reboot again to the previous kernel. In my machine it is 2.6.24-11-generic.
I don't know if this will work if you updated from other ubuntu versions. I was already in hardy.