Windows is not reading Western Digital external hard disk

I have a western digital 1 tb hard disk. which was working fine few hours ago.
but now when I am connecting it it is not showing in my computer.
I am using a windows 7 X64 machine.
I have tried every thing.
when I uninstall the driver from device manager and connect it again, windows tries to
install the driver but fails every time.

I have lot of important data on the drive
Plzzzz Helppp