I made the biggest mistake of my adult life and installed Yosemite without backing up my HDD. Fortunately, I do have most of my actual files and programs saved to my external HDD, but that leads to another problem.
I use a lot of 3rd party apps to make music, and they are not compatible with 10.10 i.e. Pro Tools etc. I formatted my HDD in an attempt to start over but it keeps reinstalling Yosemite from the Internet.
I've made several USB boot drives but when they go to load up it just gives me "international no" sign (see image below).
Can someone please help me as my work/life is tied in to my studio. Oh also my external HDD is now all of a sudden read-only NTFS instead of Mac read/write enabled.