What is wrong with my TV?

Hi when i switch my 42 inch plasma tv on there is no sound or picture. after a few attempts the tv comes on with sound and no picture. after about 30 minutes the tv comes on with the picture in green and then in blue. After 3 to 4 hours the colour comes to normal until you switch the tv off. When switched on again the trouble starts again. Please help

Faroek Seedat
July 2010