What does F4 do?
More Information. F4 is a predefined keyboard shortcut in Excel that repeats your last command or action.
Unlock/ lock the Fn key
To do this hold the Fn key down (1) and push the ESC key (2). Now you can just press the F4 or F12 button and Excel will immediately do the required action instead of requiring the Fn button pushed first.
The main function of Alt+F4 is to close the application while Ctrl+F4 just closes the current window. If an application uses a full window for each document, then both the shortcuts will function in the same way.
3: You are using a laptop keyboard
This is easily fixed! Just hold down the Fn key before you press F4 and it'll work. Now, you're ready to use absolute references in your formulas.
1) Check Your F4 key (If you are using a Dell Computer). If the light is on, then your microphone is muted in Windows.
To enable FN Lock on the All in One Media Keyboard, press the FN key, and the Caps Lock key at the same time. To disable FN Lock, press the FN key, and the Caps Lock key at the same time again.
Check if your keyboard has an Fn key somewhere. Usually, you will find it somewhere near the Space key. If yes, press Alt+Fn+F4 shortcut to check if the open window closes on your computer. More often than not, this works.
Try pressing Fn + F4. If you still cannot notice any change, try holding down Fn for a few seconds. If that doesn't work too, try ALT + Fn + F4. This should work.
The most common way to close an unresponsive app on Windows is to use the keyboard shortcut of Alt + F4. This combination of keys tells the operating system to terminate the currently active window. Use it wisely.
The FnLk, F-Lock key is a toggle key on a PC compatible keyboard used to enable or disable the F1 through F12 keys' secondary functions (hotkeys). The F-Lock key is similar to caps lock in that it "forces" F1 through F12 to use their standard functions, as defined by the program used.
Do I have an F Lock key?
Keyboards that have it usually have a light signal to indicate if the F Lock key is activated or not. If you don't have an F Lock key, you can look for the “FnLock,” which also sometimes comes in the form of a padlock with Fn written on it.
Method 1. Toggle the Fn Lock key
All you have to do is look on your keyboard and search for any key with a padlock symbol on it. Once you've located this key, press the Fn key and the Fn Lock key at the same time. Now, you'll be able to use your Fn keys without having to press the Fn key to perform functions.

The F4 on Excel is the function key that can allow us to repeat the last action as many times as we want. So if you have been thinking about what is F4 in Excel, now you should know that it is simply a function key that can help us repeat the last action in Excel.
On some Latitude systems the F4 key is used to mute the built in microphone. (See Figure 1).
If you have a light on that key (or whichever key has a blue mic with an X icon), hold Fn and tap F4. If the light stays on, your computer has Fn lock enabled, so simply hit F4 instead. If the mic and camera are set to block or ask, change them to 'Allow' by clicking on them.
The function keys or F-keys on a computer keyboard, labeled F1 through F12, are keys that have a special function defined by the operating system, or by a currently running program. They may be combined with the Alt or Ctrl keys.