Sounds familiar, I had the same problem using Mdk 9.0. For me, the solution was in the /etc/X11/XF86Config-4 file, which I edited according to the instructions of the pdf (p 26):
a Find the relevant Device section and replace the line:
Driver "nv" (or Driver "vesa")
b In the Module section, verify that you have:
c Remove the following lines, if they exist:
After this edit, X started with a nice NVIDIA logo before the desktop appears, and is stable for up to 20 minutes (no joke unfortunately). I'm still workiing on that, but as I am an absolute newbie, all help is welcome....