Unable to find driver for this platform \"ACPI\" MACOSX version: not yet set
Try starting up from the recovery partition (by holding command-R), in single user mode (by holding command-S), in safe mode (by holding shift), or in Internet recovery mode (by holding option-command-R).

If you already have backups and you can start up from the recovery partition or in Internet recovery mode, try choosing the Reinstall OS X option. It downloads an OS X installer and installs it over the current installation, keeping user files and settings in place.

If you can start up from the recovery partition but reinstalling OS X does not work, try to erase and reinstall OS X.

If you don't have backups but you can start up from the recovery partition, you can save a disk image to an external drive with Disk Utility.