If your PC is set to do automatic backups, Windows 7 has the annoying habit of creating a restore file each time you do a Windows Update, and that can eat up lots of gigs of hard drive in no time. Try this:

1. Click on the "Computer" icon (will be on your desktop if you've configured Windows 7 to show it).
2. Once open, right click on your "C" drive and select Properties.
3. Click on "Disk Cleanup" in the General tab.
4. Click on the More Options tab and select the System Restore and Shadow Copies "Clean up..." button.
5. Windows 7 will ask you whether you want to delete all but the most recent restore point. Click on the "Delete" button.

Works like a charm and I use it all the time on my PCs. You'll be surprised by how much drive space will be recovered.

Best.

Your hard drive is larger than 47GB.  It's probably partitioned with a "D" partition that can be used for installing programs and user data.