I had a Virtual Box (under Windows 7 64 bits) running for a few days with no problems.
It run updated Arch, with KDE.
Yesterday the problems started, after doing "pacman -Syu", something has changed...
From now on, when I start X, I only get a black screen.
I've traced the problem to the libgl library - if it's not installed, X starts correctly. If it's there - X fails.
In order to verify my assumption, I've installed a new Virtual Machine according to the "unofficial beginner's guide", installed X, tested it, installed XFCE4, tested it - so far all OK.
Then, I've installed audacity (it also uses libgl, and I wanted to avoid KDE to be sure it's not with them).
And now - there is this failure in the Xorg.0.log:
[ 6552.010] (EE) AIGLX error: vboxvideo does not export required DRI extension
(I wanted to attach the 2 log files, isn't it possible??)