Here is my situation. My macbook pro froze so I restarted it and ended up with the grey startup screen with OS X not loading. I have already reset the nvram and safe boot with no success. Also I tried restarting from the OS X disc and I cannot repair the disk or even erase my hardrive for a fresh install. During disk repair and disk erase it will say it cannot unmount the disk and after a few minutes of trying to reinstall OS X again it errors. Is there something I'm missing or is it a possible hardware problem? Any help is much appreciated, thanks.