Q I bought a 2 TB external drive for Time Machine backups from my Macbook Pro. On waking it from sleep, it reports that it was ‘not ejected properly’. Now Disk Utility says it needs repair, but cannot repair or initialise it, and it will not mount on my Desktop. What should I do?

A The original error is usually benign, but seems to have marked a major disk error in this case. Shut your Mac down, then turn the external drive off. Leave them for a minute or so, turn the external drive on, then your MacBook Pro. This may allow your drive to mount normally, for repair using Disk Utility.

Failing that, it is a question of how valuable the files are on that drive. If they justify the expense, and you want a commercial recovery service to see what they can retrieve from it, shut the drive down and prepare to part with substantial cash. Otherwise you can try a third-party repair tool such as Drive Genius. If there is any suggestion of a hardware problem you will need to invoke your warranty. But you will probably have to initialise the drive and start again with your backups.

Updated from the original, which was submitted for publication in MacUser volume 31 issue 3, 2015, but never appeared.