Screen Brightness keeps automatically adjusting to 100%
Since you have already un-checked the "Auto-adjust Brightness" option in the display settings, try resetting the System Management Controller (SMC). This may resolve the issues related to power management. Follow these guidelines to reset the SMC. One of the indicators that your SMC might need to be reset: 


  The display backlight doesn't respond correctly to ambient light
  changes on Mac computers that have this feature.