help my techwood 42 plasma won't come out of standby?

hi can anyone help i've got a techwood 42" plasma when switching out of standby both the media box and tv lights turn green theres a click but the picture dose not come on, some times there's no problem and every thing works but other times it takes hours of turning it on and off to get a picture can you help or should i think about a new tv many thanks

john
February 2010