HDMI "No Signal" for both Desktop and Xbox 360

I use my tv as my screen and sound for my desktop using the hdmi cable.
It worked perfectly until recently when all of sudden it stopped working and displayed "no signal".
I also got a xbox 360 from a friend and when I connect via HDMI it also displays "no signal".
I searched all over the web for solution, but couldn't find one...

I have 2 separate hdmi cable, so i'm not trying one cable that might be broken for both.
When I connect the desktop via hdmi, I hear a connecting sound from the computer but nothing displays on tv and shows "no signal". My desktop also identifies the LG-TV.

Also, after I connect the cables and I flip through the channels to get to the hdmi channel, it says "connnecting..." at the top for like 10 seconds then displays "no signal"

I have Dell SX2800 desktop and I have LG 50PX4DR TV

Please help