My Lenovo X200 laptop has developed a problem recently whereby I get a blank internal screen on booting into Ubuntu 11.10. Display works normally during boot, after which the desktop is displayed momentarily before blanking out. The gnome-shell menus are not visible during this brief flicker of desktop.

It seems that the laptop is behaving as if there is an external monitor connected and set as the primary display, without mirroring or extending to the internal display.

Here are some observations:

1. If I connect an external monitor, my desktop appears on it.




2. I can then successfully use Displays (system settings) and xrandr to turn on the internal display (which is set to off), and can then mirror or extend across both displays.




3. Once I've turned on the laptop screen and set it as primary, I can disconnect the external monitor and use the laptop display independently.




4. If I boot the laptop without an external display (in which case I get the blank screen), I can switch to an alternative terminal, e.g. tty1, at which point my internal display functions correctly, but if I return to tty7 it blanks out again, and at this stage I can no longer switch to tty1, tty2, etc.




5. I can boot into Windows without problems.

I think it's possible that I meddled with some settings somewhere in the past in order to set the external monitor as the primary display when the laptop was docked. In this case I wonder if someone might direct me to potential files that I might have modified (and remind me of the changes that I may have made), so that I can revert to the original settings. This would have been a while back though, I think, in Ubuntu Maverick or Natty (and I don't know whether such modifications would persist on upgrade). This is a recent development, though, so I think there's more to it than that.

I can't think of any software installation or changes to system files that might coincide with the problem appearing.

Does anyone have any ideas for what's going on here, or how to diagnose the problem? If there's a command I can use to print out relevant system info, please let me know and I'll update the question with the details.