I also had this issue before, apache couldn't start on localhost, so I restarted windows and it worked, thought ok, but as I always turn on WAMP services when I need and not on startup, it didn't work again, that is when I understood that Skype is using port 80 as alternative.
So now everytime I install Skpye, I remove the checkbox and don't permit it to use port 80 at all and don't have these kind of problems anymore as I don't see any reason for skype to use port 80 at all at my machine, same with 443 for https.
Usually the alternative 8118 or 8080 is also used by other services.
To check which ports are in use you can use NMAP or NETSTAT if you don't have NMAP on your computer:
In command line/shell just type: netstat -an or netstat -o
and if you have NMAP you can just call it:
nmap -sS 127.0.0.1
and you'll get the services running on ports on that ip address, which is your computer.
NMap is a port scanning tool where netstat is not.