.....and 10 notes aren't working. I swear to God I'm ready to flip my lid.

I hope paypal can assist

Have done a factory reset - no joy. Have it sitting in a warm environment now to see if that helps considering how cold it has been in transit......

Probably needs the strip under the key bed replaced.
It's a very common problem with PSRs.
DonM

Sitting in my warm kitchen with a heater relatively close seems to have done the trick!!!!!!!! Thank God. It seems OK now.

Good news! I'm glad it was that.
DonM

... wow ... just how cold WAS it ...
I remember when I played Cordovox the cold and/or humidity used to wreck havoc on the tuning ... often, when I turned on the 'tone generator' it would emit the sound of a note playing ... got to the point where I would pack a hair dryer to 'warm up/dry out' the tone generator before a gig ...

It must be cold enough to freeze the balls off a pool table, as my grandmother used to say.
DonM

You better get that Kb checked out, how used was it? previous player might have had a very heavy playing hand....check the key strips you don't want it happening on stage or anywhere ...
Ive never had that problem....& I have left my Kb in the car for months at a time in winter also..good luck with your new acquisition.

Playing it this evening to test it and it has went again. Disgusted isn't the word. I have recorded a quick video of what has happened this time.

FAULTY PSR S910

Sounds like bad (dirty) contacts that may need to be cleaned...or replaced. Did you try canned air spraying under the key bed?

If you decide to take it apart:
http://www.psrtutorial.com/music/projects/ContactStrips.html

If it were me, I'd contact the seller and if you used Paypal/Ebay you should have some protection.

I can understand your frustration
Good Luck