Hey there, Marija!
Welcome to the community!
I'm sorry to hear about your external hard drive.
HDDs are rather sensitive and usually one fall is enough to damage your drive beyond the point of repair.
My suggestion if you can still access the drive, is to back up all your files on another external or a computer because it's about to die. You most likely crashed the hard drive's head/s and it's soon to be useless, if it's not already.
The next thing you should do is contact your manufacturer for support. Check the labels on your external for the serial number, then open your manufacturer's website and use the serial number to check the warranty of your drive.
If your drive is still under warranty, you should RMA it (Return Merchandise Authorization) as soon as possible.
http://wdc.custhelp.com/app/answers/detail/a_id/8
Taking it out of the enclosure voids the warranty, so make sure you check this before attempting any disassembling.
Let us know if you need any further assistance on this!
We are here to help!