Data i wish to transfer is greyed out

Not very computer literate so forgive me but could really do with some help.

I have just purchased a WD MY BOOK ESSENTIAL 2TB i am running windows 7 and have another external hd plugged in.

I am running the applied software which is finding both the comp and the external drive.

It is backing up the external one just fine, however the on the main comp it is showing that i have 465GB under a greyed out section named system.

This obviously my main data but it wont let me copy that.

Can anyone please help?