Resurrected a 27" iMac I had replaced 2 years ago.
5 - 15 minuten
The computer would not boot up. It had starting having issues before that. I decided to replace it with a 21.5" iMac. I was concerned about the cost to repair and the risk. After 2 years, I could"t bring myself to dispose of it. After viewing the guides on IFIXIT, I decided to try to replace the hard drive myself.
iMacs can be a little intimidating to work on. It's not obvious how to open it for repair. The IFIXIT guides were helpful in this regard. Replacing the hard drive was easier than expected. I had the original OS X disk and application disk that came with the computer. I was able to boot up from the OS X disk and install on the new hard drive. I then updated from OS X 10.6.4 to OS X10.6.8. Then I upgraded to OS X 10.10.5. I now have a 27" iMac running the current OS X operating system for a very reasonable cost and a little effort.
The decision to repair or replace a computer is always daunting. At the time of failure the computer was 3 years old. I did not want to invest several hundred dollars to get it repaired. At the time, I thought it would be best to apply that money towards a replacement. In the meantime, I couldn't dispose of it. I'm glad I decided to repair it myself. The IFIXIT guides were helpful.