i too don't have any sound suggestions, just troubleshooting thoughts.... so, it's a virtual. good, copy it, register it as a new name, take a snapshot (what you should have done before doing this in the first place) and boot it up (the copy - we're not doing anything to your primary - in fact, take another copy of that and put it on a network drive, usb hdd or something for safe keeping). then, boot it up and remove X (you can go this route, or install a new system, do an ls -lR and diff after your command). either way, you can go in and totally rape a filesystem after taking a snapshot and no one really cares (unless it's production).
my second recommendation (might also try it first - though the former might be a learning experience) is to check the virtualbox tools (or whatever they call it). it's probably got a config somewhere on your virtual that might store monitor settings. the other place i'd look is in the physical configuration file that virtualbox actually uses to configure the machine. though i currently use virtualbox on my mac, i am much better versed in esx, so i can't point you to actual files, just tell you what might cause issues. let us know where you end up.
