What does a no entry sign mean
What does a no entry sign mean.
how do I get rid of it
Question marked as
It means the OS is not compatible with your system. This could also happen if the OS or file system has become corrupted or if your drive is failing or you have a bad drive cable.
https://support.apple.com/en-us/HT204156
What is the exact model of your computer? You can get this information by entering your serial number here.
What version of macOS?
Try running the Apple Hardware Test or Apple Diagnostics depending on the age of your system.