Unfortunately Youtube has stopped - Here is an easier fix.

[Ethelred]

You switch on you phone and find the message "unfortunately Youtube has stopped"
You press OK but it comes back again in a microsecond, stopping you accessing anything.
There have been many solutions offered online involving making hundreds of frustrating key presses to get into the apps menu and scrolling down to the bottom to enable the Youtube app to get rid of the popup.
Here is a much easier way:
Switch on the phone to boot up.
In between the popups, get to settings, then apps, then the 3 vertical dots at the top right which opens up a window which includes "Reset app preferences".
This will re-enable all deactivated apps, including the one causing the popup. Activate this and the popup should disappear. Job done, much less difficult than the other solution.

 

[B. Diddy]

Welcome to Android Central! Thanks for the tip, but be aware that Reset All App Preferences can be a hassle, since as you say, it re-enables all disabled apps. If a user purposely disabled a bunch of apps, that means they have to go and disable them again. It may be more efficient to try clearing YouTube's app cache and data first, to see if that works.