Issue adding PowerPivot Add-In Excel 2013

Hi all,

I am attempting to add the PowerPivot Add-In, but the option is not available in the COM Add-Ins (print screen attached).

Using
- Excel 2013 32-bit
- Win7 64-bit OS

I have followed the instructions at:
https://support.microsoft.com/en-gb/kb/2805999


Using the 'fix it for me' did not work, so I investigated manually and found that the following did not exist in the registry:

Microsoft Office PowerPivot for Excel 2013 add-in
• HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\User Settings\PowerPivotExcelAddin
• KEY_CURRENT_USER\Software\Microsoft\Office\Excel\Addins\PowerPivotExcelClientAddIn.NativeEntry.1



Any thoughts on how I can enable the PowerPivot Add-In would be very much appreciated as I don't know what else to try.

Many thanks,

David

Has anyone else come across this issue before?