Drive lights up but won't mount

WD External Drives External Drives for Mac
1

I have a WD Passport external drive. It was left plugged in to my iMac for the evening. The next day the drive was still plugged in and spinning but not mounted. Light still blinks when plugged in, drive is spinning but still not mounting. What do I do?

2

Could have got unmounted accidentally in the Disk Utility. Mount it back.