Hitachi tv turning itself off and on?

I have a hitachi 37LD8500 tv that will not stay on. it turns itself off sometimes, wont turn on other times, the led display flashes red/off sometimes.
It will work when im using ps3 with hdmi cable but when connected to sky via scart it turns on and off constantly.
I figured it was a power supply problem but when i look at the board all the caps look perect. dont really know what else to check, any suggestions?