NVIDIA CUDA problema

Hi everybody,

i have a machine mounting two nvidia controllers (from lspci)
3D: TeslaK20c (rev a1)
VGA: Quadro K600 (rev a1)

everything was fine.
The problem started when i decieded to install CUDA.
First i follwed a guide i found on the nvidia website, through rpm, i don't know if i succeded in installing CUDA, however the X server was down and i was not able to restore it.
Then, following an instruction by the redhat support team, i just tried again a cuda installation, now following this https://access.redhat.com/site/solutions/64300
but i had some problems when compiling the kernel modules.
Then i recognized that in that guide, you are sent to download the 275.19 version of the nvidia driver.
So i downloaded from the nvidia website the latest driver, 319.82 but i actually don't know if this is the right one.
However, with this driver everything went fine
Except that the X server is still down!
and it also seems that there is no CUDA anymore

any suggestion?