If the number three key is not working you may have a dead key. There are two solutions to your problem. You can either purchase an external keyboard that has a plug-in USB and use that - or replace the keyboard.
Your keyboard is disfunctional.
Your number lock key isn't on?
Probably your keyboard key is not working. Try to replace that key and try to see if it helps, else you may have to replace your keyboard as the last option...
If your "enter key" is not working then there is another "enter key" in numpad. If that is also not working then it is time to get a new keyboard for yourself. ~ESKAY-BBSR~
Solutions are chemical mixtures, and three words concerning them might be concentration, solubility, or particles.
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It is the middle black key in the group of three.
Press [Shift Key] and [Comma Key], then the number three Eg: <3
Why the window key in keyboard?
keyboard
If your keyboard is missing a key, press the key-less spot very lightly when used, or try to place the key back on, or at best get a new keyboard.
You probably just need to purchase a new keyboard - you can get them for around $10.