Why are my function keys not working properly?

Hello Ricardo, did you maybe had a spill onto the keyboard?, also if the unit is old, ( i don’t know how old) some buttons might stop working , like buttons of tv remotes, it might be worth it to open the whole thing to have a look if its dirty or worn out . if its worn out, there is a conductive glue available from specialised electronic shops, just cover the tip of the missing carbon rubber with a very thin layer of the conductive glue , wait for it to dry, reassemble. also while you have it open, maybe then you can check if bridging corresponding pad of the reset option would do anything. good luck.

Try to redownload the program. I had the same issues and it helped me. It gave me a lot of problems because I used it for education. Fortunately, this site https://plainmath.net/textbooks/ saves me from failing lessons. But maybe someone has other more smart suggestions?