AFAIK modern native Linux drivers are, as a general rule, able to start X without any configuration.
Alternatively Nvidia propritary driver needs a config, normally in /etc/X11/xorg.conf
(I think that ATI Catalyst is the same but I don't know for sure).
So, most likely you need a proper xorg.conf
Please note the error messages that X gives, _before_ the no screen found. They may provide valuable clues.
For nvidia (proprietary) check nvidia-xconfig (package and utility). It should get you started.
Alternatively nouveau (free) should not need any xorg.conf (actually it may even be detrimental to have one, may confuse the driver).
I have no experience with ATI but it should work similarly.
BOILERPLATE WARNING: make backups and ensure you have a backup plan.
PS: If you need a xorg.conf don't start from scratch, it is too time consuming even for an expert. Use an utility to generate a boilerplate config then tweak that one as needed. Last time I checked with nvidia proprietary tools as packaged in RPM Fusion non-free repo you seldom need to edit directly the config.
PS2: AFAIK the normal virtualization engine in F16 is KVM. Is quite good, see Proxmox. Alternatively look at VMPlayer (may require some simple paching). (I wouldn't mess with VirtualBox but then this is me