W8 and W10 do not always fully shutdown (so they can reboot quicker).
To ensure nothing is still running try the following
, boot into W7 and Run shutdown.exe /s /t 0 from a command prompt (or Press Windows key and R)
Try chkdsk again from Command prompt before boot. (chkdsk for C: not the temporary X:)
Try Minitool Partition Wizard and/or the Bootable CD version to shrink the partition.
What was the first OS (supplied when new) on the machine?
ie is it W7 MBR machine or W8 UEFI?
This may be important (I have only skimmed)
The old legacy boot menu may be helpful at some point? (F8 works again, nothing is loaded till you select OS)