Computer unable to recognize external HDD after installing USB-drivers

Hi!

My computer ( running 64 bit Windows 8 ) does no longer notice my external backup HDD when I plug it in to a USB-port.

a.) Could this have anything to do with the USB-drivers I had to install to get my computer to communicate with my arduino duemilanovo? If yes...

b.) ...how can I get the computer to work with both my arduino and my backup HDD.

/ Nicke