In my case this was due to skype using alternative port 80.
Temp Solution : Shut-down skype
Permanent solution :
Setup skype using different port as follows File -> Options -> Connection -> Uncheck "Use port 80 as an alternative for..."
Other problems :
most likely apache is not running, so make sure you dont' have anything in this list: IIS, Skype, Zone Alarm, NOD32, Eset, Internet Optimizer, Google Accelerator, any other database server, any other webserver?