mke48

I just installed WAMPserver 32 bit and php 5.4. I see it has the green symbol on my system tray, and if I put my mouse over it, it says 'wampserver - server offline' I created a helloworld.php file, just like mentioned at this guide: http://www.wikihow.com/Write-PHP-Scripts but the webpage says "not found: The requested URL /helloworld.php was not found on this server." anyone know what the problem is?