How do I configure X-windows on Linux with Tesla C870?

First, follow the steps as given in the installation guide that comes with the Tesla C870.   

The key is to configure your PC to first run X-windows without the Tesla C870 and then add the Tesla C870 and add it to the Xorg.conf file.  NVIDIA provides a tool called nvidia-xconfig that helps in automatically generating this file.  To use this utility, follow these steps:

If the system has a non-NVIDIA graphics card, then configure X to run with the non-NVIDIA graphics card.  Then add the Tesla C870 and run nvidia-xconfig.

If the system has a NVIDIA graphics card, we recommend the same procedure as above or you can directly run nvidia-xconfig.

If these two steps do not work, then run “nvidia-bug-report.sh” as root and post the “nvidia-bug-report.log” on the CUDA forums for Linux to get additional help. 

CUDA on Linux forums