boots to log in screen, Blue screen, back to login

[daboogymahn]

HELP! my mac has worked fine for first few months. i turn it on and everything is normal. then it gets to login screen. it can tell me my password hint and everything, but when i type in my password it goes to a blue screen for 1-5 seconds and then returns to the log in screen.

[Bobjob186]

boot your mac in target disk mode, backup all your important info, reformat your drive.

[djb21au]

After much hunting around I discovered this post and solved a similar problem without having to reinstall: http://dltj.org/article/macosx-launchservices-login-loop-fix/

Probably a bit late for daboogymahn but hopefully of use to others who might strike this issue.