Chosen Solution
Trying to boot to a mac os yosemite usb stick, every time it fails, :/ Also whats the highest macOS it can run, ALSO thanks in advance :]
When trying to make installer the 2nd time
Sounds like you may have not prep’ed the thumb drive correctly. First you need to format it using a Mac with a GUID Journaled file system. Next you need the correct OS installer copied to it. The highest your system can handle is macOS High Sierra (10.13.x) but I strongly recommend sticking with Sierra (10.12.x) as High Sierra alters the file system from HFS+ to APFS which does not run too well on older SATA based drives. Get the installer from here: How to get old versions of macOS older installers have an expired certificate. Follow this guide to setup the installer onto the thumb drive How to create a bootable macOS Sierra installer drive Last step if the drive won’t boot up on its own with the thumb drive, time to restart your system and press the Option (⌥) to get to the startup manager so you can select the thumb drive. Reference: Mac startup key combinations
A prohibitory symbol, which looks like a circle with a line or slash through it, means that your startup disk contains a Mac operating system, but it’s not a version or build of macOS that your Mac can use.
