Yamaha Psr e313 stays on power button contact OK has no effect.

Question edited for clarity.

Try a Factory Reset. Try a power reset first. Disconnect from the mains plug for 15 minutes.

System Reset - Yamaha PSR-S750 Service Manual

ManualsLib https://www.manualslib.com > ... > Service manual
There are two reset methods in the SYSTEM RESET display: Factory Reset and Custom Reset. ... This function lets you restore the status of the instrument to the ...

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  Yamaha PSR-S750 Reference Manual - System Reset

  https://www.manualslib.com > ... > Reference manual
  This function lets you restore the status of the instrument to the original factory settings. ... buttons to enter or remove the checkmark. ... operation for all ...
  
  

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You may need to perform a factory reset operation. Turn power off, hold down the DEMO button and turn the keyboard back on. The
screen should display 'Setup is initialising'. This will disappear after a few seconds and the screen will display its default. If that does not work you may need to re-install program disks, I think you should have 6 of them

Tom is probably right, the carbon contact on the switch wears out. Open the case and replace the switch.
Part #40
Price £ 3.95 + postage if required

Check that your power adapter is 12 volts DC AND MOST IMPORTANT is the center pin is positive... this is reversed of MANY adapters used for pedals, etc. The current rating should be around 1.5 amps. Don't take another techs word for it... check it yourself.

MR SATISH IF YOU WANT TO SOLVE THIS PROBLEM CONTACT:9887070565,94136768(ANAND NARWAL)FROM RAJPUTANA ENTERPRISES

My keyboard yamaha psr2000,so I want parts silicone rubber keypad 61 and including electronic board,thank you.

rubber contact strip requires replacement

from what you say the humming is caused by large capasister which maybe leaking so could well be a power supply falt
or mabe dry wire
o/c on audio maybe
you need engineer freind