Casio electric keyboard, two keys only make sound once! Please help!

I have an old Casio WK-500 keyboard that I had lying around the house and didn’t use until now. Every key works fine except for the B flat and B keys on the furthest right of the keyboard. I’ve taken apart the keyboard to dust and clean the inside as much as I can, but the furthest I’ve gotten is this: when I first power on the keyboard with the adapter, the keys will work the first time I hit them, but then every time after that they do not work. So in short, I can only get the keys to play only one time. I don’t think it’s a problem with the volume, because the display doesn’t even register me playing those two keys.

So in short, I can only get the highest B flat and B keys to play one time after powering on, and if I want to play them again I have to wait for a while, then all of a sudden they work, but only ever one time.