If you have an Nvidia card it most probably has to do with the shoddy, latest WHQL drivers: version 285.62.
Revert back to the previous driver release (280.26) to rectify the problem.
This worked for me (I have a gtx570 and my tv is also connected to my pc) except I subsequently found out that I absolutely NEEDED the latest driver release from nvidia to be able to play Battlefield 3! -.-
Cheers