Apple Hardware Test gives no issues, but MacBook 8,1 fails to load after login This MacBook fails to finish logging in after boot ... diagnosis was a "bad harddrive cable", but after replacing that, no change. For reference, an independent, Apple-certified repair center did a "long" diagnostic after the "Genius" (term used only due to branding) bar said the hard drive was bad.

The laptop boots to a login prompt. After successful login, a progress bar that looks like a firmware update or system check takes a long time to complete (>15 min), and then the computer shuts off. I'd like to reclaim the current OS install, and avoid reformatting/reinstalling.

How can I diagnose what is wrong, without being able to login? AHT "long" test shows no problems.

Bonus points: how can I run the same diagnostics the Apple-Certified repair center did, so I can see the error codes, etc...

Update:
Disk Utility in repair mode failed to verify or repair the disk.
Problems were found with the partition map which might prevent booting
Problems were encountered during repair of the partition map
Run Disk Utitiy from Recovery Mode. On Reboot, press Command (⌘) R. Open Disk Utility. Your partition map might be corrupt. Hit repair a couple of times.
Reset NVRAM/PRAM.  http://support.apple.com/kb/PH18761
Also run EtreCheck and post the report here. Free Download:
http://etresoft.com/etrecheck.