Why my External hard drive Isn't working?

I have a Western Digital - WD Combo (USB / Firewire) External Drive. I recently disconnected it from my deskyop to my laptop but I didn't disconnect it the right way. Instead of disconnecting the correct way, I just pulled the cords strait out and reconnect it to my laptop. I repeated it again to connect it back to my desktop but when I did that, nothing wont happen. The computer wont read the External Hard drive. Is their anyway to get it working again.