Is the 2nd hard drive a brand new one? If so Windows probably needs to initialize it so you can create a new simple volume.
Click Desktop tile from the Start screen to go to the desktop.
Once on the desktop screen, press Windows + R keys simultaneously to initiate the Run command box.
On the Run command box, in the available field, type COMPMGMT.MSC command and press Enter key.
On the opened Computer Management snap-in, click to select Disk Management under Storage category from the left pane.
From the lower half section of the right pane, right-click Disk 1 that represents the second hard disk drive attached to the computer.
From the displayed context menu, click Online.
Once done, right-click the unallocated disk space in order...