Another commonly-suggested panacea, Safe mode has its uses, if you understand why it is ‘safe’.
Safe mode
All the useful key combinations, arranged by function rather than keys.
What to do when your Mac won’t start up, and is acting dead, or at least mortally wounded.
When I started my iMac up, the fan has run up to be really loud. How can I fix this?
The Eclectic Light Company 