After plugging in the pedal, my Williams Overture digital piano suddenly won't play.

It sounds like there may be an issue with your Williams M Grand digital piano. The fact that the display is not working and the piano is making a buzzing sound suggests that there may be a problem with the internal electronics.
Here are a few things you can try:

1. Check the power supply: Make sure that the power supply is working properly and that the piano is receiving power. Check the power cord, ensure that it's properly plugged in and that the outlet is working.
2. Check the connections: Make sure that all of the connections between the piano and the power supply are secure and that there is no damage to the cables.
3. Try a factory reset: Consult the piano's manual for instructions on how to perform a factory reset. This can sometimes fix issues with the internal electronics.
4. Check the manual: Consult the piano's manual for troubleshooting steps, it may have some information that can help you.

If none of these steps work, it is likely that there is an issue with the internal electronics and the piano will need to be repaired by a professional technician.
Keep in mind that attempting to repair a digital piano can be dangerous if you're not familiar with the proper procedures and safety precautions. It's best to let a professional technician handle the repair.
It is recommended to contact the manufacturer's customer service or a professional technician to have the piano inspected and repaired.
Regenerate response

Sounds like either there is a problem with a low frequency driver or perhaps an eq setting.
If you have an external (line) output, you can try sending the signl through another amp. If you have headphones, then try them also. If the headphones sound distorted as well,then see if you have the eq to high on the bass.
Other than that, it could be a filter capacitor in the power supply. You would need some experience fixing that.

You have to plug in the laptop sorry to say. Think of it as a piano that can be used as a midi controller.

Theres no reset that i know of. Have you checked the power box (plugs into the AC outlet) voltage and that it is working as it should?

Holding the page up and down buttons while powering on supposedly resets it. I have no sound except demos, but no lights showing like yours, and williams tech support said to reset that way but it didn't seem to do anything. Good luck hope this helps!

Pianos do NOT respond to keys pressed hard... they respond to FAST presses. If you have an issue with the piano, first go on record to activate your warranty. Most of these electronics DO have a setting that adjusts the "feel" which affects the loudness versus key velocity... Now here is a secret??? Shh... The manufacturers turn up the demos just like the advertisers turn up the commercials on the TV... I would suggest looking for the adjustment of feel, and if that doesn't get satisfactory results, find another and compare yours to another... if yours is still underperforming, exercise your warranty for repair or replacement.

First thing is to check the connector is fully seated... sometimes most of the contacts make but one might not. Beyond that, contacts in the pedal are next suspect.

Assuming this has worked in the past (otherwise if you have changed to different pedal that is the problem) the usual thing is the machine samples the state of the pedal at power up and assumes the polarity of the pedal is at rest. Make sure you are not pressing it as you power up. Also verify the pedal is COMPLETELY plugged in... sometimes they are not quite fully in and that causes a problem, especially with the two stage versions that are sometimes used.

Here is a link:http://www.williamspianos.com/products/encore.cfm If you don't have one, download the manual. If it still doesn't play correctly with the pedal connected according to the manual you will have to contact them to see about servicing. The information is also at that link.

The ROLAND pianos USUALLY require that you use a normally closed sustain pedal.

MANY pedals are the opposite and close when pressed. SOMETIMES you can open the pedal and reverse the way the switch works.