I had the same issue and found that once you place (or make modification to) the php.ini in the system path you need to manually stop and restart all IIS services...
From a command line run:
net stop iisadmin
This will prompt to stop web, ftp and smtp if installed.. Say, Yes.
Once all service are stopped, start each service individually with:
net start w3svc
net start msftpsvc
net start smtpsvc
(No need to restart iisadmin, as it will restart on its own.)
Works for me, good luck.