My Lumia 520 has lost all icons only a clear screen is visible, except for calls. What could the problem be?

[WPCentral Question]

My lumia 520 has lost all icons only a clear screen is visible but if you call i may recieve

My Lumia 520 has lost all icons only a clear screen is visible but if you call i may receive

 

[charlatan1978]

Re: My lumia 520 has lost all icons only a clear screen is visible but if you call i may recieve

Have you tried a soft reset?
Failing that a hard reset?
Also are you running WP8.1 or W10M? Is this the result of a failed upgrade?