A CRC error means the drive failed its cyclic redundancy check. In other words, the computer couldn't read the drive properly.
The first thing to try is to see if the problem is with the USB slot or USB cord you're using. Use a different USB slot or a different USB cord and see if you have better luck. I'm assuming your external drive connects by USB. If it connects by Firewire or eSATA, you'd have to change those cords instead of the USB cord.
Assuming that's not the problem, and if it's a regular hard drive (not an SSD drive), it's possible a utility like Spin-Rite could recover the information on the drive. https://www.grc.com/sr/spinrite.htm
Of course Spin-Rite costs money, but if the information on the drive is important, it may be worth it. Make sure you have enough space on another drive to copy the information off the bad drive to. How SpinRite works:https://www.grc.com/sr/whatitdoes.htm
There may be a free drive recovery utility you could find, though it's unlikely to be as thorough as SpinRite. It may be all you need though. A lot depends on where the bad part of the drive is.
One trick, which sounds odd but sometimes works for people, is to put the drive in the freezer for a few hours. It works for some drive problems, not others. It generally works just long enough to get your data off (when it works).
If you do manage to get your data off the drive, assume it's bad and don't trust it again. Consider the guarantee for consumer-grade hard drives is no longer than 5 years and often less, and save your data on at least two external hard drives in case one goes belly up.