Go to Start-->Run-->diskmgmt.msc (run diskmgmt.msc, this will bring up the Disk Management tool).
See what you need to do there, you will have to create a partition and give it a drive letter, which you can do in dskmgmt.msc. You may even have to initialize the disk first, but you will certainly have to create a partition on it, give it a drive letter, then format it as NTFS.