I was in the process of upgrading my 2007 iMac, my second Apple purchase and what really got me into the Apple ecosystem, to Mavericks when I ran into an error. After a lot of turning off and on, and stalled boots and system checked, I learned that my hard drive was about to and did indeed fail. Fortunately nothing of any significance was on the computer as I had transferred everything to another computer a few months ago. But, I felt like, as it was the top of the line in 2007 and had a perfectly good 24 inch monitor, that it had at least a few more years of life in it.
The repair went swimmingly, thought I avoided a step or two in the guide to make it easier on myself. I dragged my brother into the process and had him hold the monitor up so I didn't have to unplug it ( one of the trickiest steps, to unplug and plug it back in, according to the guides ), and that worked quite well. I wasn't expecting the force with which I would have to use to get the HDD out of its dock, but once it was gone, I put in the bay adaptor and a SSD and now it seems just as fast as my new rMBP. It's like a whole new machine!
If you can, avoid unplugging the monitor so you don't have to plug it back in. Get a friend to help, or use a stick or box or prop to keep it up. Also, make sure when re assembling to have the bottom of the outermost frame on the computer properly, otherwise your screws won't line up and you'll have to redo that process again.
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