Letters sometimes won't work

I assume you have a desktop system with a plug in keyboard; if you have a laptop please tell me and I will type up instructions on how to clean the keyboard on laptops.
You might want to try cleaning out the keyboard.
Unplug the keyboard and hold it upside down; shake it gently and allow debris to fall (pressing the keys can help).
I would also either use compressed air or a small computer vacuum on the keyboard.
Let’s see if this working…if not we might need a through cleaning.

nnh