This usually happens on a VPS. WAC must be showing a message box behind that screen. Please use the taskbar to bring the message box in front.
If the message says " Configuration failed to initialize" then you need to do something about it :
1) If you are using windows server 2008 - Open server manager - click add roles - select application server and install it.
2) IF you are using windows server 2003 - Open server manager - click add features - select .net framework 3.5 and install it.
After it is done start WAC again and it will work properly.
If issue still remains create a ticket above to allow us to help you.