Using a new WD HD in my old WD 'My Book' USB interface - how?

I have a 1Tb Western Digital My book which holds WD10EAVS disk. Problem is, is that I have bought another 1Tb Green WD10EZRX disk to act as an additional backup, assuming that I could just plug in the existing 'My book' USB interface and use it.
I apply power and the lights come on but I cannot get into it. I can go into basic details in 'drivers and devices' and it tells me it is detecting it fine but I can't format it and certainly can't save any data to it.
What can I do to resolve this?
Tom.

Have you Initialized the new drive?

All sorted!
The main problem was that I'm on someone else's computer so had to be signed into their admin account.
Anyway, went into the Windows 8 'computer management' section, initialised it and I was able to format.

Cheers,
Tom.