I posted a message about this as well over here
by accident instead of in this thread. But I'm having the same problem with Mandriva Limited Edition 2005. It happened, though, after I did a live update type thing to update sofware packages. It worked fine before.
I too use an nVidia card. I'm going to poke around and try some of the suggestions too. Hopefully something worked. But I think it's a config problem. Something shutting down display 0: before X can grab control over it, from what I saw in my error messages (in the other post). I'm not sure.