http://music-mix.ew.com/2009/12/01/snoop-dogg-gps/

Who needs a screen anyway!

I had this happen a year or so ago on a Server 2003 box and never could find the actual cause. I don't know if the fix is the same in this case, but in my case it was simple:

Check out [HKEY_USERS\.DEFAULT\Control Panel\Colors] - if everything is set to [0 0 0], modify those values to something other than black. The easiest thing to do, actually, is to export that key from another box that's good, then import on the box that's got the problem.

I only come across it occasionally, but several times I have found myself wishing for LEAST and GREATEST functions in T-SQL, like in Oracle. Of course people always suggest creating workarounds via a CLR addin, functions or CASE statements. But really, in both cases, this seems like a trivial feature to implement. C'mon MS!