Do you have an Nvidia card, or AMD? Unless things have changed in the last few months, AMD requires HDMI 1.4a (it's not always specified on the product if it is 1.4a or just 1.4). Nvidia on the other hand, will work with 1.3 (or 1.3a, not sure).
I've got an AMD 6870 in CF
Note: When I said my TV said 1.3b I have a FEELING it was incorrect on the LG site.US site said 1.4 but for my region said 1.3b even though the model no. is the same.Though strange enough the TV sold in my region has LED Local Dimming as a native feature whereas in the US model it has to be unlocked.