If you try running the Diablo III Setup.exe file and nothing appears to be happening, check to see if the Windows Service for Secondary Logon is enabled. The game requires it and will not run if it's disabled.

To check, open Control Panel > Administrative Tools > Services (or Control Panel > System and Security > Administrative Tools > Services) and scroll down to the Secondary Logon service. Right click it and select properties. Make sure the Startup Type is NOT set to Disabled. Any other setting should be ok, although we've seen a couple reports of a user needing to use "automatic."

Be advised that some security programs, such as AVG, may be switching this service off by default.

This service being disabled may also cause the system to appear to hang during the "Updating Setup Files" portion when run.
Edited by Machkhan on 5/16/2012 4:26 AM PDT