Why won't my "F" keys work? I try to use F1 for help or F11 to make my browser full screen and nothing happens.
My guess is that you have a newer Microsoft or Logitech keyboard. These have something called an "F Lock" key located just above the number keypad on the right side of the keyboard. It allows your Function keys to do more than one operation. If you notice, the top side of the keys probably say "Print", "Undo", "Save", "Reply", etc. while F11 and such are on the front. You may have an indicator light that comes on when you are in normal "F" mode.
When you boot up your computer the F Lock key is off so the keys use their "enhanced" function. What that means is that every time you boot up you need to hit the F Lock key for your Function keys to act normally. I don't know who the genius in Redmond is who came up with that idea. Microsoft offers no way to change this setting.
Keep all this in mind if you need to boot up in safe mode (F8 key) or BIOS (F2 or F10). You must immediately hit F Lock when you turn on your computer, then the function key—hoping that you do it all in time.