You'll have to be a little more specific.
Which Samsung 840 drive are you using, an 840 EVO? What operating system are you using? Is this a new drive or a previously used drive?
The drive may be formatted in a way that Windows (which I assume that is what you are using) does not like. Plus, you should use disk management (in Windows 7) to work with the partitions. You can launch Disk Management by typing "disk man" in the Start Menu search box and selecting "create and format hard disk partitions" - providing the fact that you are using Windows 7.
Be very careful here - the hard drive that you booted from and its partition are in the list that you see.