Comment 5 for bug 309482

There is a page for debugging blank/black screen issues at http://wiki.ubuntu.com/X/Troubleshooting

There is currently a known bug with usplash that can cause a black/blank screen issue (on -intel at least), however that is confirmed due to a usplash change on 4 feb, which is later than this bug report so not likely to be the cause.

The error message in comment #3 is just saying that there was another X session running. Make sure to kill all X sessions before starting a new one.

The fact that the issue isn't seen with -nvidia doesn't prove it is an -nv issue, but it is an okay assumption for now. -nvidia and -nv are very, very different, with completely different dependencies and interactions with the xserver, so the root problem could still lay in something other than the driver. But we can start here.