Sony STRDH800 emits a loud humming noise cuming throu speakers as soon i switched on and after 3 minuts av reciver switched off byself and blinking protected......plz help

Check the source of humming noise. Disconnect the input cables of source one by one. A faulty source should be found. It may be the source or the cable connecting from source to receiver. If a faulty cable, replace it & if it is source, repair it. Also try connecting a separate earthing for the receiver. A separate earthing stud is normally provided in receiver for separate earthing. If none of these solution work then you will have to look inside the receiver for loose earthing from various PCB's especially preamplifier.

It is possible that the amplifier had encountered a fault with a higher current drain which had triggered it to a protection fault condition. The fault can be your output drivers- the MOSFETS/IC's fitted for both the channels, Use a meter after disconnecting to check for short in the drivers. Disconnect the positive and negative voltages to the output and see if the protect changes. Even a fault in the preamp stages that drives in high current into the output can shut the Amplifier. Sometimes this can be a noise like a HUM or HISS before the protect works. Faulty capacitors in these circuits also can cause similar issues and needs close observation.
You need to confirm and replace the specific stages or outputs. If not there can be issues in the mother board, maybe the protect circuit by itself is shutting off due to a faulty bias , maybe a leak in any voltage/current sensing circuit. Also disconnect the speakers and test, if the protect is off then check for short on the speakers.