Hello mad00lini,
Does your WD external hard drive make any clicking or buzzing sounds?
Since you dropped your drive, there has most likely been some physical damage, thus making it disappear as a storage device from your PC.
Can you see it in Disk Management and Drive Manager? Where in the OS is it visible? If it's not visible in the OS, can you see it in BIOS?
Depending on the answers I would suggest you try and scan the drive with the WD Data Lifeguard Tool:
http://support.wdc.com/product/download.asp?groupid=810&lang=en
If that's not possible I doubt that the drive would be able to be saved. Hardware malfunctions or damages can sometimes be more dangerous to your information than software ones. If you can't access the drive in any way or even scan it to determine damage state, I suggest you take it to a Data Recovery Company to get your information.
This is a list of WD's official Data Recovery partners:
http://support.wdc.com/recovery/index.asp?wdc_lang=en
I wish you best of luck!
CK_WD