No signal to external Display/LG LCD TV

I own a Macbook Air 13" (Late 2010) and used to connect it via Mini-Display-Port to HDMI-Cable to my LG 37" LCD TV. While on Snow Leopard everything worked fine. Now I upgraded to Lion and I am not able to get a signal to my TV. The MacBook Air lists my TV in the display settings but I cannot get a signal to my TV. I tried ever resolution and setup but it does not work. I also tried to delete the com.apple.windowserver.plist and resetting PRAM, nothing worked. Can anybody help me with this? Greetings from Germany.