I had this happen once before, but last time it just started working....
All the HDMI inputs on my 42PFL3704D/F7 quit working. I have a popcorn hour and an xbox plugged into inputs 1 and 2. One day I'll turn them on and they won't work, even though they were the day before. unplug the tv, popcorn hour, and xbox for an hour (power and HDMI) plug them back in and still nothing...

Also, I did just check and have the most current version of firmware (from 2010-03-15)