Because it needs to be initialized or formatted or both.
Control panel, administration tools, computer manager, disk manager. See if it shows in there.
You should get a popup saying this drive needs to be initialized. IF not, right click on the drive letter itself to initalize it or right click on the empty space and make a new partition.
Yes, it's there. Shows unallocated but online. If I right click it, a window pops up saying, New simple volume, sew striped volume, new spanned volume. (and of course, help and properties).
There is no drive letter next to it.