HOW DO I SHUT THIS COMPUTER DOWN. MY X is gone?

Answer 1

On most small computers, pressing and holding the power button for a few seconds will force a shutdown. This (or turning off the power supply, or taking the final option of the "110 reset" by literally unplugging the computer) is not a "clean" shutdown, but it may be your only option if the computer is otherwise unresponsive.

Short of that, you might try one or more of the following to see if you can bring the computer back to a responsive state so that you can shut it down more cleanly.

Esc
Alt-F4
Ctrl-Alt-Del

You might also try logging in remotely and issuing whatever the computer's shutdown command is (you didn't specify the operating system, so it's hard to be more specific on this, but some variation on "shutdown" is pretty common).

Answer 2

Simultaneously press the CTRL ALT and DEL keys, and click on the symbol to the bottom-right of the screen that looks like a circle with a vertical line through it.