How to Test Your Keyboard
Simply press any key on your keyboard. If the key lights up on the virtual keyboard above, it's working correctly. Keys that don't highlight may be broken or stuck.
FAQ
Some keys don't register?
Some key combinations are blocked by the OS (e.g., Win+L, Ctrl+W). Also, very cheap keyboards may have key rollover limitations where pressing 3+ keys simultaneously causes some to not register.
What is N-key rollover?
NKRO means every key press registers independently, no matter how many keys you press simultaneously. Most mechanical keyboards support this; cheap membrane keyboards often don't.