Where is the MachineKeys folder in Windows 7?

In clean installation of Windows you can find it under C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys

In newer versions of Windows, try: %SystemDrive%\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\MachineKeys

C:\Users\All Users\Microsoft\Crypto\RSA\MachineKeys

And make sure the folders are not invisible.