Genymotion

Genymotion is based on VirtualBox, most issues come from VirtualBox. If you cannot start a Genymotion emulator, try reinstall VirtualBox, or repair VirtualBox.

Resolving Genymotion problems on Mac

sudo /Library/StartupItems/VirtualBox/VirtualBox restart

open Disk Utility (search Spotlight), try Repair Disk Permission

Restart Genymotion