For some reason, my GPU has completely stopped outputting HDMI it seems.  It detects that a monitor is there and makes the effort to try and display things, but the monitor doesn't actually receive anything.  Could it be my mini hdmi to hdmi converter?  I noticed that when I screwed around with that by bending the cord I got the screen to say "check signal cable" instead of "no signal" for a little bit (It displays no signal when it detects that the computer is there, then says check signal cable if the is disconnected).  I have also gotten it to nearly display for a bit when jiggling the cable.  I have a GTX 560, by the way.