Hey there, lea_01.
Would you please post a screenshot of what you see in Disk Management about the drive (you can use imgur.com to upload the image)? Here's how to open it:
How to access Disk Management in Windows to manage hard drives.
Other than that I'd recommend that you try the drive with a different USB cable (preferably not longer than 12"-18") and a different computer, to see if the same thing happens. If you are able to get the drive recognized, please backup all the important data you have on it, just to be on the safe side. After that you could download its manufacturer's diagnostic tool and test the drive for errors, to see if anything out of the ordinary pops-up.
Hope that helps.
Boogieman_WD