Maybe it's a video driver problem... MCE asked me if it should install the latest 3D Nvidia driver. I answered "yes". Maybe it didn't install the legacy version of the Nvidia driver....
Similar thing happened here, if I try to startx manually, I see:
Error: API mismatch: the NVIDIA kernel module has the version 1.0-7185, but
this X module has the version 1.0-9639. Please make sure that the kernel
module and all NVIDIA components have the same version.
The old system I'm trying to put this on is an Nvidia Vanta...
If you haven't tried to use Adept to upgrade the nvidia driver, you can probably get X working again by logging in and overwriting the configuration file...
cd /etc/X11
cp xorg.conf.pbackup xorg.conf
If you have made the mistake of fooling around with the video drivers (like I did), this will get X working again:
sudo nvidia-glx-config disable
I tried using Envy, but there is an easier way (in my case, anyway)...
Upon a fresh install of Kubuntu, you might notice a small message from down by the clock that says you don't have proprietary drivers installed (or similar). If you click the program's icon in the tray by the clock (move over them all until the find the one), you can get it to install the proprietary drivers from nvidia... it correctly detected and used the legacy drivers on the system I was using, although X would only come up in 800x600 instead of higher resolutions. I suspect that's not hard to fix, in any case, with the drivers in place, LinuxMCE no longer asks to install the video drivers, upon install... so it's installing (rather slowly) now...