macbook pro encounters prohibited sign while booting with USB
In verbose mode, you will find that OSX gets stuck at:


  Still waiting for root device


This error usually happens when your media used to boot OSX is not detected properly and can't be mounted. You can therefore try these methods to get it to work:


Changing the port you insert your USB into
Remaking the bootable media
Getting a new USB


If all fails your device may need special drivers of some sort. You can also check it out with an Apple Genius.