I have a MacBookPro OS X 10.7.5 from 2011. When trying to boot it has a slow startup or login, with numerious spinning wheels. Sometimes after a long time I can sign into the computer and sometimes it just fails to startup or login.
It became more serious recently as I think I might have let my battery run out. Once it did boot and I also tried to download the operating system to reinstall it but it allways stops around 1.4 GB out of 1.7 then the wheel spinning started again.
Now it wont boot at all, so I tried to boot in in safe mode. After the shift key it took about a half hour until the time bar at the bottom filled up, and when it did the screen went black. When it hit the start button it went back to the safe startup screen with the gray apple, spinning wheel and bar filling up at the bottom.