Alt - Up keyboard Shortcut Stopped Working

Yes one of my favorite Vista keyboard short cuts has stopped working. I have done no registry manipulation. I did install Sun's VirtualBox and even switched the Host key to Alt for a moment before deciding to switch it back to Right CTRL. Can anyone help please.

Thanks!!
Brian

I found the answer, I set shortcut to answer calls in Skype to Alt Up and this is why the Alt Up Vista shortcut stopped working!