Out of the blue, my iMac (late 2010, running El Capitan) started refusing to boot. The progress bar would take forever to reach 100%, and then it would just stop there once it reached it; all the while the fan running loudly.
I am able to boot into Recovery Mode, and I can even run Disk Utility (it doesn't detect any problems.) However, when I attempt to reinstall the OS, it tells me:
This disk has S.M.A.R.T. errors.
This disk has a hardware problem that can't be repaired. Back up as much of the data as possible and replace the disk.
I have an outdated Time Machine backup, made before I upgraded from Mountain Lion to El Capitan. Most of the data in the backup is the same, but there are a few GBs of new files I'd like to backup as well.
Since Disk Utility tells me everything is okay, am I able to somehow mount an external, and backup files? Possibly through Terminal? And If I were to use the drive with the old Time Machine backup on it, would I have to delete the backup before writing new data to the drive?
I'm not very computer savvy, but I can manage my way through Terminal with a lot of instruction. So please, try to answer in terms I will understand. Thanks.