iMac would try and boot but could not find the Hard Drive. I tried repairing the disk, sometimes the hard drive would be found but, while trying to reload operating system I would get an error message.
Replaced the hard drive, the process of changing the hard drive was actually pretty easy, especially after watching your video guide. all in all , the hard drive change out from start to finish was about an hour. This was the first time I had even thought about taking our computer apart. I honestly thought that because it was an iMac the parts were going to be crazy high priced (I was soo wrong) Thank you for the video guide and the cross reference parts, and the low price.
Don't be afraid of a bad apple, take your time, use the right tools and you can do it
and of course check with ifixit for help and parts