Sharp AQUOS LC-26P50E television. Stuck on 'Standby'/'Sleep'

I have a Sharp AQUOS LC-26P50E television. When I power it up at the set (having plugged in and turned on at the socket), the green 'Power' light comes on as it should but then it switches to the 'Standby' (red) light, there is a click and the 'Sleep' indicator starts flashing, alongside the 'Standby' light (now also flashing). The only way I can get them both to go off is by powering off at the socket. I have tried following the 'System Reset' instructions and this turns off the 'Sleep' light (and stops the 'Standby ' light from flashing), but then both of them start flashing again as soon as I try to take the set off standby. Help, please!