@sbotalla , if you have a fast WiFi connection, you can simply use Internet Recovery to format and reinstall to either the latest OS X for your Mac, or the factory version.
'''Start up from macOS Recovery
macOS Recovery installs different versions of macOS depending on the key combination you press while starting up. Hold down one of these combinations immediately after pressing the power button to turn on your Mac. Release when you see the Apple logo or a spinning globe.
Reinstall the latest macOS that was installed on your Mac, without upgrading to a later version.1
Upgrade to the latest macOS that is compatible with your Mac.2
Requires macOS Sierra 10.12.4 or later Reinstall the macOS that came with your Mac, or the version closest to it that is still available.