Do any of these commands work from an Elevated Command Prompt? See the first link for what the commands do.
defrag c: -a -v
defrag c: -v -r
defrag c: -v -w
How to Perform a Full Manual Defragmentation of Your Hard Disk Under Windows Vista
http://www.howtohaven.com/system/vistadefragmentation.shtml
Windows 8 – Elevated Command Prompt
http://www.tweakhound.com/2012/11/12/windows-8-elevated-command-prompt/
Returning to Windows 8 is easier said than done thanks to Microsoft damaging the Windows 8 Recovery Partition.
How to uninstall Windows 8.1
http://www.lohud.com/usatoday/article/3476743
How to uninstall Windows 8.1
http://howto.cnet.com/8301-11310_39-57610729-285/how-to-uninstall-windows-8.1/
Windows 8.1 Update Leaves OEM Owners With Broken Restore Function
How to Create Recovery Media before Installing Windows 8.1
http://windowsitpro.com/windows-8/how-create-recovery-media-installing-windows-81
Update to Windows 8.1: FAQ
http://windows.microsoft.com/en-in/windows-8/upgrade-to-windows-8