Q I have three external hard drives, one of which stores my Time Machine backups. Since moving them to my new iMac, I keep getting alerts that they are ‘not ejected properly’, the disappear, then return again. What is wrong with them?

A This should not happen, of course.

With your Mac shut down, check and reseat all the cables connecting the hard drives. If you have alternative cables which you know are trustworthy, try connecting with those. Then power your drives up, let them run up to speed, and start your iMac up.

Most external drives do not require any special software, but some models from certain vendors rely on drivers to support additional features. If yours need any such drivers, check the vendor’s website for any updates.

If they should work fine but continue self-ejecting, check the Energy Saver pane: do not put your hard disks to sleep, as that can sometimes lead to external drives being ejected in this way. Unless they are intended to be put through many stop-start cycles, putting them to sleep is probably only going to risk making them fail early.

If they eject even after that, immediately afterwards, open Console and see what event is recorded in the logs when they were ejected. Normally the logs will contain a reason for the ejection occurring, and should help explain what is going wrong.