Tv turns on for few minutes then turns off?

Well i can turn my tv on and it works fine for around 2 minutes then will turn its self off? I then have to unplug the tv wait 5 minutes and then plug it in and it does the same thing again ive opend it up no sign of damaged capacitors or anything no burn marks oil marks or anything like that its boggleing my mind!? Someone please help i have a samsung 40" lcd tv model number is LE40B620R3WQXU thanks in advance!