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.
Best Answer
The "invalid node structure" and "disk I/O" errors you see in verbose mode are both indicative of a failing hard drive.
The invalid node structure points to a problem with the data cataloging mechanism of the operating system, basically that system that keeps track of where all the data is stored. One off reports of this aren't so bad but coupled with the issues you're seeing and the other error message I imagine it's a result of a failing drive.
The Disk I/O error pops up when the hard drive is inaccessible, either for a split second or several minutes. This can usually be attributed to any of the following:
Because the disk is temporarily unavailable you often see system corruption (such as the invalid node structure error above) occur as a result.
So, what to do from here...
Hopefully that helps or at the very least gets you started.