Id presume you check on that program thats opened disk management if your hard drive says free space available and shows ur missing gigs. or if its partitioned is there a blank partition.
i found there is a little thing that says unallocated and its 104.83 gb i right click on it and an option either to do primary or extended partion comes up what should ii do
erm.. I beleive u`ll want to make an extended partition as a primary is just for operating systems. might want to format the unallocated space first though but be careful! lol