Trying to boot up on Mavericks USB Install Drive, receive prohibited sign on screen I have a late 2011 Macbook Pro and I had Mavericks, which ran just fine, but I upgraded to Yosemite after hearing some good reviews. I didn't back it up in time machine. It made my laptop extremely slow and glitchy, it's practically unusable now. I followed this http://www.macworld.co.uk/how-to/mac-software/revert-back-mavericks-from-yosemite-3581872/ to try to downgrade back to Mavericks, and I believe I successfully made a bootable Mavericks Install Drive. Everything worked just as it should have, I shut down my computer, pressed alt while turning it on, and chose the USB drive. It loaded for a few moments but then in place of the apple symbol, it just showed a prohibited symbol (circle with slash through it).

I tried to repair the drive in disk utility but I had no luck. If anyone could help me figure out a solution or find an alternative I'll be very grateful!
I've had mixed success using that bootmaker utility.  Try Apple's instruction here

https://support.apple.com/en-us/HT201372

Assuming a) the 'install osx mavericks' file is in the Applications folder and b) your USB drive is named MyVolume, open Terminal and run this command. 

sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Mavericks.app