As a tech person I get asked questions like this all the time. First, check to see the color of the letters on the function button, which usually are Fn or FN. See what the colors on the rest of the keyboard are, the function button is usually a different color than the rest of the keyboard letters and numbers are. I have seen anything from blue to aquamarine to red to orange to brown to black when the keys are on a pink laptop and the letters are white. Make sure that the function key is not on when you are pressing the shift key (or the 4). The function key enables the ability to change the brightness settings, the volume, enable numbers lock and disable Wi-Fi among other things.
If this doesn’t work then try updating the laptop’s keyboard drivers. If that doesn’t work try remembering when the last time everything worked the way you wanted it to, and go into system restore and restore the laptop to a previous date when it worked the way you wanted it to.
I can’t count how many times I have accidentally done this myself and then asked myself WTF when things go back to normal. One way you can tell if the function button is on is if you plug in an external keyboard and it works fine.
I hope this works.
~Life never happens the way we plan, which forces us to change our paths whether we want to or not. If we don’t learn to adapt to the changes that are put in front of us, the change may end up becoming downright painful. We don’t have to like it but there may come a time when we have to accept it because change comes whether we want it to or not. ~ Unknown Author