Machine not powering on - Raspberry Pi Black Screen

▶  Description of the problem

Your screen is frozen and shows the Raspberry Pi logo.

The screen looks like this and you can't do anything:

▶  Possible origin

The OS of your Raspberry Pi has probably been corrupted. 

This usually happens when users switch the power off without shutting the computer down the proper way (Raspberry>Logout > Shutdown).

▶  Solution

Follow this procedure to reset your machine completely and reinstall the OS on the Raspberry Pi.

In the future, always turn off the machine by going to Raspberry Logo > Logout > Shutdown and wait a few seconds before switching the power off.