I have tried to unistall revit 2013 on Windows 8.1 through the control panel nothing happens. So then I tried to uninstall manually through microsoft fix and revit 2013 is not listed so I click and that option and the next box says put in the product code.What product code am I suppose to use?
have you tried
msiexec /x {7346B4A0-1300-0510-0409-705C0D862004}
or
msiexec /x {8D37F1B6B9A808A40A4EA9F594394577}
this is from the registry
HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\Revit\Autodesk Revit 2013\Components
Alternately if you have the original USB/CD/download you can frind Revit.MSI and right click select Uninstall.
I do not have Revit Architecture/other flavors , but at least this will give you idea where to look
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Products\0A4B643700310150409007C5D0680240