go to computer management, click storage, click diskmanagement, click ur drive(the space where its white, kinda a representation of ur disk), right click it, click format, follow instructions.
do u got the disk that came with the drive? if u do, pop it in, boot to the disk(havent used mine in a long time) select ur drive, and format it(i think)
also, what comes up on the menu when u right click the unallocated space on it?