If it's a new dive then the problem is likely that it hasn't been partitioned and formatted yet. If so, you need to start up Disk Management:
-> Start
-> Right-click "Computer"
-> Select "Manage"
-> In the Left pane of "Computer Management", click "Disk Management"
Locate your new disk in the LOWER portion of the middle pane - you may have to scroll down to find it. Right-click it, create a volume and format it.