Prohibitory sign showing on Mac startup

While trying to install OS X El Capitan there was a brief power cut mid installation then the Mac tried to restart it first brought up the apple logo then brought up the prohibitory symbol. I can't get safe mode and I have done a hard restart all with the same thing can you help?

Solution 1:

Sounds like the system files are corrupted, still try to boot into Recovery Mode by holding the Option key at startup until you see graphics of hard drives. Select Recovery with the arrow keys, then press Enter. Recovery mode will allow you to reinstall the OS.

Solution 2:

Most likely a kernel panic, where vital system files are missing. Boot to Recovery Mode by holding Command + R at startup. If you have any backup drives (Time Machine), you can reinstall OS X using these drives, or fresh install. If your machine does not have a Recovery partition (older models), then you will need to replace the hard drive.