Hello if you are using Skype then from Skype Tools->options->Advanced->Connection in this check Use-port there one text box may be there default port using 80 so make that box empty. and save logout from Skype and login again now your skype use port other than 80 so now your Apache is working fine.
And there is other solution is also you can also change your default port for Apache 80 to other from Apache
ServerName localhost:80 to any other free port like
ServerName localhost:81 may helps you.