Are you getting prohibitory sign Mac OS X ? It is a start up warning given by your Mac system at the start up indicating that something is wrong with you system. It can be due to hardware malfunctioning or or firmware corruption. Generally you will see a gray apple logo and a presentation of prohibitory sign is followed after few seconds. This means the system has recognized a valid installed OS but can not boot because of some problem . There are few things you can do to fix Prohibitory Sign Mac OS X, one is to boot the system in safe mode as it will ignore some kernel extension which are not properly configured. Another option is to reinstall the operating system which will overwrite the previous setting to default in order to fix prohibitory sign Mac OS X. If you can not fix the problem by these methods then you will need to use a third party software that can tackle the situation by restoring the original setting files to the default location. Luckily this is fairly straight forward task to avoid prohibitory sign Mac OS X by using the software with all application and data intact.