I seem to recall, that there was a 15GB partition, but in all the years I've installed Windows, I've never partitioned a drive.
You can use diskpart from DOS. This is off the top of my head, so if you have any trouble let me know and I'll look it up.
Boot to DOS
LIST DISK [ENTER]
SELECT DISK (# OF THE DISK YOU WANT TO FIX) [ENTER]
LIST PARTITION [ENTER]
SELECT PARTITION (WHICHEVER ONE LISTED YOU WANT TO DELETE) [ENTER]
DELETE PARTITION [NOERR] [OVERRIDE] [ENTER]
SELECT DISK (#OF THE DISK YOU WANT TO FIX) [ENTER]
LIST PARITION [ENTER]
Make sure no partitions are listed.