iMac shutting off while booting at 50% progress

1) Try a safe boot.

Shutdown your machine. Hold down the shift key. Poweron. Wait awhile; wait awhile while you harddrive

is being checked.

http://support.apple.com/kb/ht1455

2) Another way to correct filesystem problems is into single use mode.

This page will tell you how to get into single user mode.

http://support.apple.com/kb/HT1492

Basically, you hold down the command + s key then powering on your machine. The command key

has a little apple symbol on the lower left. It is between the alt/option key and the space bar.

It comes on, no chimes, Apple Logo on Screen,

I expect you to get the chimes since you get the apple log.

when I mounted the device with /sbin/fsck -fy

disk0s2: I/O error

** the volume Macintosh HD could not be verified completely.

This doesn't mount the disk, but does a disk repair. The disk repair failed.

Do you have a backup of your data?

no. You need to get a disk recovery utility if you data is important to you.

I believe you need to replace the disk drive. I'd worry about the no chimes. Could be something in addition or besides the bad disk.

--------------------------------------------------------------

You need an external hd to recover you data.

Perhaps Disk Warrior will be of some help:

http://www.alsoft.com/DiskWarrior/

"Stellar Phoenix Macintosh - Mac data recovery software, recovers data from damaged, deleted, or corrupted volumes and even from initialized disks."

They have a trial version, so I guess you can see if your data can be recovered...

http://www.stellarinfo.com/mac-data-recovery.htm

"Data Rescue II is the best data recovery software on the market for recovering files from a problem hard drive. Data Rescue II works when other tools fail. Data Rescue II is also completely safe to use since it does not attempt any risky repairs to the drive while its scanning."

http://www.prosofteng.com/products/data_rescue.php

FileSalvage is an extremely powerful Macintosh application for exploring and recovering deleted files from a drive or volume. FileSalvage is designed to restore files that have:

-- been accidentally deleted.

-- become unreadable due to media faults.

-- been stored on a drive before it was re-initialized/formatted.

http://subrosasoft.com/OSXSoftware/index.php?main_page=product_info&products_id= 1

"TestDisk is a free data recovery utility. It was primarily designed to help recover lost data storage partitions and/or make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally erasing a partition table)."

http://en.wikipedia.org/wiki/TestDisk

Wondershare Data Recovery for Mac

"Recover lost photos, video, documents, email and archive files from any Mac-based hard drive or external hard drive, iPod, USB drive, SD card, digital camera, mobile phone, and MP3/MP4 player, due to accidental deleting, formatting, virus infection, improper operation, unexpected power failure, and other unknown reasons. Also, iPhone recovery allows you to recover lost photos, videos, SMS, contacts, note, calendar and call history from iTunes backup file. With the free trial, you can preview all your recovered images, videos, music, documents and archive files prior purchasing this Mac Data Recovery."

http