you have a damaged file system and it cannot be repaired. to find out why reboot while holding down command+R and in recovery mode open disk utility and try to repair the disk. It will tell you why it cannot be repaired.
It may be that you need to replace the disk or just reformat it. you will need to format it as HFS+ for you to be able to install on it. you will lose all data on the disk! back up your data before reformatting
report back here after figuring out why the disk cannot be repaired and i will update my answer.