I have a yamaha mpv 5 piano it will come on but no sound when played.

For the best info contact Yamaha support. Here's the link-

Digital Pianos Keyboards Guitars Drums Live Sound and Music Production...

It sounds like the piano is in mono setting. One note at a time can be played. Find out how to set it at poly mode, allowing multiple notes to be played at the same time.

Unplug and leave it unplugged for a while and then make sure the plug is nice and secure on both ends and try again

Perhaps the performance assistant technology is turned on.
Press the [PERFORMANCE ASSISTANT] button to turn it off.

Have a professional tune it for you. It may be that some strings have loosened/tightened.

It sounds like you have a part overheating and failing, then cooling off and starting again. i would take it into the nearest Yamaha repair facility or contact your local authorized repair to come take a look before it goes out of warranty.

Although the keys have a weighted feel, this is not because of a system involving connection t hammers as in an acoustic piano. This is done mechanically, however, which would indicate a need for cleaning. If you have an authorized Yamaha service center in you area they would need to do the cleaning.

See if the sound is present at the headphone jack by plugging in headphones. This is the start of testing.

My opinion is you should take the instrument to a yamaha authorized service center.. It's doubtful this will be user serviceable, particularly if the problem isn't on all the keys, and the service center will have access to the parts needed as well as more information from Yamaha than they will share with an end user.

I have a Yamaha P200.

One thing I noticed is that it is the hardest electronic keyboard I have ever played. The action is pretty close to a real piano but it is the hardest action I have experienced.

Could you just be a bit out of practice or not recalling accurately what is was like to play it?

Or of course it could be gummed up with crud if it wasn't covered or in it's case while you weren't using it.

There is definitely a sound when the key come up after being played - you could call it a thump or a click I guess. Again it could be a crud issue as well.

Having it cleaned could be helpful.