Stuck in OS X 10.90 (14A299l)

Maybe it's to late but I might help anybody other.

Go to "System" -> "Library" -> "Core Services" and open "SystemVersion.plist" (with TextEdit). I once changed the value of the Product Version to "10.9" to make my matlab run. So I forget to change that value back. Just type "10.10" and everything should be fine.

If you have another Mac available to you, download the Yosemite Installer onto that, then follow these instructions to make a bootable Yosemite Installer flash drive: Create a bootable installer for OS X Mavericks or Yosemite - Apple Support and then boot from it by following these instructions:

• Backup your computer using Time Machine: Mac Basics: Time Machine backs up your Mac - Apple Support
• Turn up your computer's volume so that you can hear it well.
• Reboot your computer, and when you hear the "Ding", press and hold the Option key
• Once the Startup Manager appears, plug in the flash drive you used for the bootable installer.
• Once the drive titled "Install OS X Yosemite" appears, navigate to it using the arrow keys and boot up from it with Enter/Return.
• Once it boots up, choose "Install OS X Yosemite".
• Follow the onscreen steps.

Hope this helps! Reply if you have any questions or need more help!

This is exactly what happned to me! Stupid school.... gave us this workaround for matlab but never told us to change it back after the semester.