Hi Paul,
Sounds like we're getting closer. I guess any program includes
your browser as well, since most of what you indicated was
MS Office except notepad.
On my laptop the Page Up and Page Dn buttons have Fn
functions of Increase and Decrease Volume. Click on the
speaker taskbar icon and then see if those buttons work in
their Fn mode. If they have a different function test whatever
it is.
A test to see if it is hardware would be to attach a keyboard to your
laptop and see if these keys and the other keys work on the auxiliary
keyboard.
If is the laptop keyboard only, pop off the key covers over those keys
and take out the hair and crud. . Vacuum over the entire keyboard
before popping the key covers back on. For a laptop lift up the mechanism
then carefully place the cover centered over the key straight down until
it pops on doesn't take much pressure.