Here is the simple 5 step process we follow when this happens to our plasma tv. It works every time.
1) Completely unplug EVERYTHING connected to the tv, including HDMI cables
2) Press and hold the power button on the tv for 10 seconds
3) Plug power cord ONLY back in to TV
4) Turn tv on.
5) Plug in all other cables at this time.
It is helpful to use a good surge protector with this tv. It still goes out occasionally but not as much.
If the process does not work, wait longer (like an hour) after unplugging everything