Every now and then I’ve had the experience where I remote into a server using RDP and after logging in I get a black screen.

After some searching I came across something that worked for me: use control+alt+end, then close the RDP session and launch another one.  This 2nd time connecting I got my desktop back. 

Rob Kraft was the one who came up with this, so credit to him:  http://social.technet.microsoft.com/Forums/en-US/winserverTS/thread/31b681c5-3658-45a5-8158-a0a0f967c4a2/