Q: I updated my MacBook Pro with a 500 GB hard drive a gigabytes of memory everything works good then try to update from snow leopard ... I updated my MacBook Pro with a 500 GB hard drive a gigabytes of memory everything works good then try to update from snow leopard to Yosemite I get a white screen with zero with a line through it turn computer off and then back on same thing more
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Helpful answers
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Feb 15, 2016 6:28 PM in response to WMROWANby leroydouglas,Prohibitory symbol
When you see a circle with a slash symbol instead of the Apple logo, it means your Mac couldn't find a valid System Folder to start up from.
If you're using your Mac at a school or business, it might be trying to start from the wrong version of OS X. Contact your IT department for more help.
If this is your personal Mac, try reinstalling OS X by using OS X Recovery.
Other options: http://www.cnet.com/news/managing-a-prohibitory-sign-at-os-x-bootup/