I have Samsung UE65MU6405 TV and i had no problems before when directly connecting my PC to TV with PC MODE. But i just bought new AVR Onkyo TX-SR494 which i now pass trough the HDMI cable.
So my problems is that normally pc mode seems to be selected by editing the icon and selecting the PC one (geez, wouldn't setting be better choice to do this?). But now TV seems to auto-detect it as an Home Theater System and as soon as i select the PC icon it reverts back to HTS icon so i cannot enable it.
So any tips on how could i enable it? I contacted samsung live chat support and they only insisted that it was feature and this is how it supposed to work 
