Can't Install Hyper-V Windows 8.1 Pro

I have a 64-bit version of windows 8.1 pro running on a modern machine. virtualization is enable is BIOS.

I cannot install Hyper-V. Windows goes through the well-know routine of

 1)"adding features"; 
 2)"cannot add features" 
 3)"undoing changes". 

This seems like a common problem, but since its a Windows system issue, you can only get a precise diagnosis if you get someone form the Windows NT team to look at your machine in person... sigh. All you can do throw various junk at it and see if it sticks. Here's what I've tried:

1) use the DISM.exe tool to verify image itegrity, or whatever.

2) investigate the max filter [drivers issue][1]. 
   Turns out windows 8 puts no effective limits on filter drivers.

3) uninstall antivirus (the potential solution to every problem)

4) I do not have a working recovery patition on my system 
  (reinstalled from usb, and naturally windows did not bother create its 
   magic partition"). Can that be a problem here? 
  As far as I can tell it is impossible to create a system recovery partition.

First Warning and first Error from Windows Update log:

WARNING: Failed to get Wu Exemption info from NLM, assuming not exempt, error = 0x80070490
Handler FATAL: UH: 0x8007045b: EnumeratePackages failed in CCbs::CalculateCUL

I've also tried looking at the CBS log, but there are way too many errors there. Here is error that caught my attention:

2015-01-13 02:59:54, Error    CSI    000000ce (F) Done with generic command 2;   CreateProcess   
returned 0, CPAW returned S_OK
    Process exit code 5 resulted in success? FALSE
    Process output: [l:73 [73]"Trying to install VMS_PP ...

  ... failed. Error code: 0x80070005.

Has anyone else come up against this problem? Anything else I can try? Thanks in advance.

Right, I'm an idiot. I had VirtualBox installed. Removing virtualbox allows for the installation of Hyper-V. Solved.