Your system may be running excessively slow and/or you want to use the Repair Disk option in Disk utility but it is greyed out. The option will be greyed out in Disk Utility whilst the operating system is running as it can not run a repair when the drive is in use. Additionally a disk repair may help you if you are not able to reach the login screen.
Repair Disk Errors:
- Turn the computer on and hold Cmd + S (to boot into single user mode) until you see a black background with white text.
- Once the text has stopped scrolling press Enter.
- Type in fsck -fy and press Enter.
- It will now do a disk check, if it is successful it will show a message like:
- “Macintosh HD has been repaired.” or “Macintosh HD has been modified.”
- Once complete, type reboot and press Enter.