Please click on WAMP icon select Apache -> Service -> Test Port 80 // this will check if the port is used by any other program
Also do this select Apache -> Service -> Install Service // this will make apache use port 80 if already not used by any other program like IIS or Skype
Restart the WAMP see if the problem is fixed or reply back in comment
Edit: If port 80 is already used by some program, then you need to change the listening port for WAMP. To do this -
click WAMP icon -> Apache -> httpd.conf
Now find listen 80 or something like that
Now change that to something else like 3333, but this time make sure you type localhost:3333 or 127.0.0.1:3333 while using WAMP.
If you want to put WAMP on port 80, uninstall the program that is using port 80 and then do things stated in step 2 also check httpd.conf file for listen [port] line