black screen after installing the nvidia-modprobe package

I’m trying to install cuda 7 on ubuntu 14.04.
Following the steps in the instruction, I got the “black screen” problem after exec “apt-get install cuda” and reboot.
However, after uninstall cuda, everything returns ok again.
To find the problem, I decide to install the packages one by one.
first , “apt-get install cuda-tooltik-7-0” and reboot. OK!
then, “apt-get install cuda-drivers” . black screen!
So, I uninstall it and reboot , OK!
At last , I found the problem in the package nvidia-modeprobe
after exec “apt-get install nvidia-modeprobe”, I got blackscreen.
After uninstall it ,everything is ok.
I’m not sure how to fix it. HELP! THX
The driver version is 346.

Here is some more info.

dkms status
bbswitch, 0.7, 3.13.0-55-generic, x86_64: installed
nvidia-346, 346.46, 3.13.0-55-generic, x86_64: installed
nvidia-346-uvm, 346.46, 3.13.0-55-generic, x86_64: installed

Did you remove nouveau?

I run “lsmod | grep -i nouveau” and get nothing.
So , maybe it’s not the problem.

You might have conflicting driver installs. I don’t know the history of your machine, whether you have ever installed any other driver, or which driver install methods you may have previously used. Have you followed the instructions for handling conflicting install methods in the linux getting started guide?

yes, this is my first time to install cuda 7 on the machine. so , as the guide told “This will not affect systems which have not had cuda installed previously”

you mean the nvidia driver should be not installed before I install cuda7?
Because the driver is already included in the cuda 7 package?