Function keys are a useful part of a Fujitsu laptop's keyboard, allowing commonly-taken computer actions to be initiated with a single click. They can open programs, play or pause music, navigate Windows Explorer and more. If they stop working, though, they become worthless. If they become assigned to the wrong actions, they become even worse than worthless, executing an unwanted action every time you click them. There are a few common reasons this could happen. Fixing these will reset your function keys back to the default settings.
Ensure that the NUM LOCK key is turned off. If you see a green light on the key or by the "NUM LOCK" label at the top of the keyboard (depending on the model of laptop), this means it is on. Click it to turn it off.
Ensure that the F LOCK key is turned off. Like with NUM LOCK, if you see a green light on the key or by the "F LOCK" label at the top of the keyboard, turn it off.
Restart the laptop. If it has been running for a long time, it could be a simple glitch that rebooting everything will solve.
Upgrade your keyboard driver. If all else fails, this restores the keyboard to factory default settings. Fujitsu offers the latest drivers on their website (link in Resources).