IMac will no longer startup, is my HDD corrupted?

Question

Hello,
As a result of a problem i have bee totally unable to use my computer for anything and work has been extremely difficult.
Recently I have been encountering a problem which occured occasionally when trying to turn off my imac in wich a grey screen would appear with a message telling me to manually turn off my imac from the power button. I continued to do this for  a while when it occasionally popped up, and once more this happened, but when i started up my mac the next day a loading bar appeared underneath the apple icon during boot. A few seconds after what I assumed was an update finished, the imac crashed and turned off. I turned it back on multiple times and attempted the process, whatever it was doing again and again.
As i could no longer access my Macintosh HD without it trying to load this bar and crashing, i held down Alt upon startup and selected recovery HD to run disk utility to see what was up. I verifyed the Hard drive itself and it told me that all was fine, however if i attempt to verify the "Macintosh HD" no matter how many ways I do it, I always end up with a few messages and the ones in red tell me "there is an incorrect number of threads", "invalid volume directory count", "(it should be 208010 instead of 208009)" and finally "The volume Macintosh HD was found corrupt and needs to be repaired." then "Error: this disk needs to be repaired. Click Repair Disk"
If I try to reapir the disk i always get the same result, Disk Utility attempts to repair the volume three times before telling me;
"Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files."
I can't access the disk to backup my files and therefore i do not want to have to erase it, so i tryed the reinstall os x option instead, to see if reinstalling mountain lion was the problem, however when i want to choose where i want to install mountain lion the disk is greyed out with the message "this disk is locked".
I am currently stuck for solutins as i had not set up a time machine to back up my files as i didnt have an external hard drive and therefore can't restore from a backup and i am reluctent to simply erase my disk as i just have too many files; music, documents programs, photos etc and it would be absolutely destroying if I had to erase them all completely.
What should I do? Is there anyway to save all my stuff before simply jumping ship? Any pointers appreciated.

Answer 1

It sounds like you've tried all the usual methods of trying to fix things but, unfortunately it sounds bad, especially as you have no backup plan in place.
I fear your options are limited and that you may end up having to do an erase and install with the unavoidable consequence of losing your data.
There are professional services out there that can try and retrieve your data (normally expensively, and with no guarantees), as well as software you can buy that may or may not help.
There is also Disk Warrior (www.alsoft.com) which has a good reputation for resuscitating failed drives - again there are no guarantees and I think it costs around $100.
Maybe someone else will spot this thread and have some other suggestions.