How to fix a failed Mac login

Client's Macbook Pro 8 installed with OS X 10.7.5 Lion would boot up with out any chime, display the user login, but the cursor would just spin without completing the login process.

The client didn't have a backup so our first goal was to get a backup of the drive. That proved a bit of a challenge as it would not mount under any other system prior to v10.7.5. The system booted fine into the Disk Recovery partition, which allowed the disk repair to be run, however it found no issues.

We eventually were able to create an OS X 10.8 boot drive that allowed us to mount the failing volume. The drive was then backed up, but during the process we discovered on of the files was incorrectly reporting its file size over 3 Exabytes. We then ran the Disk Tools repair again, but this time using OS X 10.8. The utility was able to correct the corruption of the file size.

We still had issues logging in at this point, but with a backup created, we then decided to reinstall the OS over the top of the existing system. After several hours, the system rebooted to the original login and we were able to login successfully.

One option we did not try was to boot to the recovery partition and then attempt to create a new login from the terminal. This might have been quicker, but we would not have been able to repair the drive corruption.

You may be wondering about why the system chime didn't work. There was nothing actually wrong with the sound, the user just had the volume turn off and because we could not login we could not reset the volume until after the user's login was repaired.

So what caused the issue in the first place? We suspect that the user deleted several system files, which we later found in the trash.

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