This page is about physical aspects of the keyboard: there’s a separate section on using the keys.
Keyboards are effectively grids of switches that make connections in a circuit when the keys are pressed. If there’s no electricity, pressing a key won’t do anything. So keyboards need power. If your keyboard isn’t working, check it’s either connected, or has batteries that aren’t empty.
There are three types of physical keyboard:
Keyboard connected by a cable
The cable provides a route for the power supply, and the signals indicating which keys you’ve pressed. Keyboards that connect using USB are common.
If your computer uses a dedicated keyboard port (PS/2), by convention it will be coloured purple.
If your cable keyboard isn’t working, check that the cable is connected at both ends.
This must have a its own power (typically AA or AAA, batteries). Some keyboards have a small light indicating that the power is on, and sometimes there is a small switch too.
The power supply of a wireless keyboard drives the transmission of data to the computer (typically using Bluetooth). When the batteries start to run out, the signal will be weaker, and the range will decrease until it can no longer connect.
If your wireless keyboard isn’t working, check that it is switched on, and that it has batteries that have not run out. You might require a dongle to be connected to the computer.
A laptop’s keyboard is integral to the machine, so it is directly connected to the power.
It is possible to connect other types of keyboard to a laptop too. If you do this, both keyboards may be active, so be careful not to accidentally press keys on the one you are not using.