How do i fix a dead key on my casio cdp 220r keyboard?

It sounds like you may be experiencing issues with the sustain pedal on your Casio CDP-100 digital piano. The problem may not be with the pedal itself, but with the internal connections or circuitry of the piano.
If you're unable to factory reset the piano and it's not responding to the sustain pedal, it's likely that there is a problem with the main board. This is a complex issue that may require professional repair.
However, before giving up on it, you can try the following steps:

1. Check the connections: Make sure that all of the connections between the pedal, the piano, and the power supply are secure and that there is no damage to the cables.
2. Check the power supply: Make sure that the power supply is working properly and that the piano is receiving power.
3. Try to update the firmware: Check if there is a firmware update available for your piano on the Casio website. Updating the firmware may fix the problem.
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 the problem is with the main board and it will need to be repaired by a professional technician. Unfortunately, this can be an expensive repair. 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 important to keep in mind that the piano was second hand and you were aware of a problem with it and you have been given a lower price as a result. It is also important to note that buying second hand musical instruments may have hidden issues, which is why it's always advisable to inspect it thoroughly before buying it or to buy from a reputable seller who can give you a warranty.
Regenerate response

Troubleshooting on a similar model here, but unless you are an electronics engineer, you will need a Casio Service Centre

https://www.ifixit.com/Wiki/CASIO_CDP-230R_Troubleshooting

https://www.google.com/search?q=Casio+COP-100+Digital+piano+no+sound

..

https://www.youtube.com/watch?v=vX_CzYD6w94
https://www.youtube.com/watch?v=3nXtmoErQk4
http://www.adultsitelinks.nl/n8fxjwh/4yupvz2.php?kevoctvxh=88-key-keyboard

Try this first with the piano off, run the control from stop to stop rapidly several times. The object is to clean off any dust deposits and shine the contacts inside the pot. If the pot is not damaged beyond repair, then this should fix it.

is it under warranty ?
if not
you may have to contact your point of sale to find their local repairer

if you cant un stick them yourself that keyboard will have to be taken apart

are the two keys ... white keys or black ...nearby or way apart
do the two keys drop loose..and lift up
or stay down
example will vacuum cleaner suction help lift the stuck keys or not

sales blurp says this
A spring-less hammer system
Scaled Hammer Action Keyboard

https://www.jbhifi.com.au/musical-instruments/casio/casio-cdp-120-digital-piano/91120

have the power checked at the piano end of the cord to rule out the adapter.

Normaly this can be a battery problem or the capacitors are getting worn out

Casio CDP has Auto Power Off: 30 minutes after last key operation, Auto Power Off can be disabled.
Please read the manual.

If it turns itself off while playing, I would try to buy a new AC Adapter to test. DC cable of AC adapters are often broken internally after much "bending".

Old reply so hopefully it's fixed. Dust or hair can get through the gaps and land on or near the contacts of the electronic key sensors. To be on the safe side (rather than doing a diy) take it in to the technicians. They'll have it fixed in a jiffy

Here is the manual for it http://casioelectronickeyboard.danielcadams.com/cs44-p-stand-cs44p-casio-electronic-keyboard-user-manual/