Monitor/HDMI problem

Hey Everyone,

I having a Problem with My LG Flatron Monitor, I recently bought a HDMI cable for it (after reading how much better they are) now when my computer goes into sleep mode the monitor says Check Signal Cable, when I move the mouse and disable sleep mode it all goes back to normal, I have tried a different HDMI cable and get the same results. any idears?

Any Help would be Much appreciated Thankyou!