My Roku appears dead.

The Green light is on and the only way I can get it to go out is either unplug the unit or hold the 'On' button in for a few seconds. As soon as I realse the button the light comes on again.
The unit will not boot or display anything on the screen and will not turn OFF.
the only way I can get the light to go out is to unplug it.
I have seen lots of posts on here about dead PSU but mine doesn't appear to be dead as I have a green light.
Any ideas?
Cheers
Marcus