Try the two following steps to ensure your computer is really not working:

1. Is the screen on ?

Check that the green LED is constantly on as indicated under point 1. If not press the power button on the far right side. If nothing happens check the power cable.

2. Is the computer on ?

Check that the green LED is constantly on as indicated under point 1. If not press the power button as indicated under point 2. If nothing happens check the power cable.

3. Common issue

This is not the power button (1). The power button is as shown under point 2.