ERROR HISYSDWN C/133 A 0000 EN YAMAHA PSR 2000 ??????

SOURCE: some of the keys do not play on our Yamaha

The key contacts have gotten dirty. The contacts are CONDUCTIVE rubber pills that are pressed onto circuit traces on the circuit board under the keys. Onehas to dis-assemble the keyboard very carefully noting the size and location of all the screws and using great care of the cables that connect the top and bottom of the case.
when you remove the keys, you will find silicone rubber strips with the black pills underneath, two pills per key.
Clean these with ONLY 99% isoprophyl alcohol and Qtips as well as cleaning the circuit board traces they contact.
Carefully re-assemble the keyboard.

SOURCE: Getting an error message when starting the PSR 2100

I would do a factory reset. Search Google for: factory reset PSR 2100.

It will be holding certain buttons or keys down when powering on.

SOURCE: 3 keys don't work on my Yamaha PSR-150 keyboard.

yes. you must change keyboard pad, below the keys, and check for dirt and deteriorated board.

SOURCE: 3 keys non function on Yamaha PSR 3000 sometimes

rubber contact strip requires replacement

SOURCE: Yamaha psr-280 flashing display no

Your adapter should be a 12 volt DC delivering 2 amps (2000 ma). If the adapter is too small, you will have the symptoms you are seeing. Make sure the polarity is correct. DO NOT use the so called "universal adapters".