suddenly, a bunch of keys stopped working on the Z keyboard. so many that's it's now impossible to type anything. about 7 out of the 26 letters won't do anything and two of the digit keys. the keys that don't work are not all next to each other, but they are very popular keys and maybe they just wore out?

i could take it apart to clean it, but it does not seem to be the place where dirt can even enter. does anyone have an idea about what I could do?