Why won't my Mac start up after downloading OS X Yosemite?

[iMore Question]

Mac was fine until I downloaded the free upgrade. I'm having major problems my PTSD is hurting my ears ringing please someone help me

 

[Just_Me_D]

Please read the information found via the following iMore Blog article. Hopefully, it'll will be useful to you.

OS X Yosemite: What you need to know before installing | iMore