There is some other program listening on port 80, usual suspects are
1 Skype (Listens on port 80)
2 NOD32 (Add Apache to the IMON exceptions' list for it to allow apache to bind)
3 Some other antivirus (Same as above)
Way to correct it is either shutting down the program that's using the port 80 or configure it to use a different port or configure Apache to listen on a different port with the Listen directive in httpd.conf. In the case of antivirus configure the antivirus to allow Apache to bind on the port you have chosen.
Way to diagnose which app, if any, has bound to port 80 is run the netstat with those options, look for :80 next to the local IP address (second column) and find the PID (last column). Then, on the task manager you can find which process has the PID you got in the previous step. (You might need to add the PID column on the task manager)
C:\Users\vinko>netstat -ao -p tcp
Conexiones activas Proto Dirección local Dirección remota Estado PID TCP 127.0.0.1:1110 127.0.0.1:51373 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51379 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51381 ESTABLISHED 388 TCP 127.0.0.1:1110 127.0.0.1:51382 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51479 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51481 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51483 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51485 ESTABLISHED 388 TCP 127.0.0.1:1110 127.0.0.1:51487 TIME_WAIT 0 TCP 127.0.0.1:1110 127.0.0.1:51489 ESTABLISHED 388 TCP 127.0.0.1:51381 127.0.0.1:1110 ESTABLISHED 5168 TCP 127.0.0.1:51485 127.0.0.1:1110 ESTABLISHED 5168 TCP 127.0.0.1:51489 127.0.0.1:1110 ESTABLISHED 5168 TCP 127.0.0.1:59264 127.0.0.1:59265 ESTABLISHED 5168 TCP 127.0.0.1:59265 127.0.0.1:59264 ESTABLISHED 5168 TCP 127.0.0.1:59268 127.0.0.1:59269 ESTABLISHED 5168 TCP 127.0.0.1:59269 127.0.0.1:59268 ESTABLISHED 5168 TCP 192.168.1.34:51278 192.168.1.33:445 ESTABLISHED 4 TCP 192.168.1.34:51383 67.199.15.132:80 ESTABLISHED 388 TCP 192.168.1.34:51486 66.102.9.18:80 ESTABLISHED 388 TCP 192.168.1.34:51490 74.125.4.20:80 ESTABLISHED 388