OK I just ran a test and something weird happened. I shut down the computer and plugged out my monitor. Then restarted with just the HDMI to DVI wire plugged in (from pc to tv) and it worked perfectly. The picture came up on screen and didnt flicker.
Then thinking the problem had been solved I replugged in the monitor and now the tv is flickering again. This must suggest some problem with settings but I dont have a clue what it could be.
EDIT: I just tired the '50 hisense by itself again and it works but only as far as the dell load up screen. Then the flickering on and off starts