help to shrink drive c w/400+ g's free space but see only 900+ MB's

I've just updated the pc specs for this thread. It's a XPS 15 about 2 months old and is the first laptop I've ever owned or used.
It came with a 500 G. hard drive of which 102 MB's are the OEM Partition, 19.53 G's for Recovery and 446.13 G's for C drive. C drive has 403.33 G's free space.
When I try to shrink C drive so that I can make another partition I'm told I only have 931 MB's that I can shrink out of 456853 MB's total.
Also it says that I can't shrink a volume beyond the point where any unmovable files are located. I defragged but it did no good.
Any help would be appreciated.
My skill level remain s that of novice.
Thanks.
H

You need the Partition Wizard bootable disk, available free here:

https://skydrive.live.com/?cid=b0a22789320e3247&sc=documents&id=B0A22789320E3247!215

Download it and burn it to a disc. Then boot from it.

It should let you shrink the partition more than Disk Management.

Back up your data before using it.

ignatzatsonic, Thank you for the help. I'm going to try it this afternoon.
Regards.
H.