I'm running Ubuntu 12.04 and my problem arises when I use CTRL+ALT+F# keys in VirtualBox (Windows XP guest).
Unfortunately, I have a number of CTRL+ALT+F# key shortcuts set up in a Windows application, which I am so habituated to using that I find myself doing so despite my best intentions not to, most frequently CTRL+ALT+F12. The screen goes white, rather than presenting a terminal interface, which may (my research suggests) be because I have a Nvidia graphics card (I don't know whether I'm using the Nouveau or Nvidia proprietary drivers).
Google and Askubuntu tell me these key combiations are intercepted by the host and are taking me to a
tty terminal and that I should be able to get back to the GUI using CTRL+ALT+F7. I can't, however, CTRL+ALT+F7 has no effect and in fact the only solution I have found is to do a hard reset.
I'm fairly new to Ubuntu, so please bear with me on this. Many thanks for any assistance.