what is using port 80 ? maybe the windows IIS service ?
when there is no need for IIS shit .. disable/uninstall it
to change apache port do following (i expect u r using xammp)
go in folder /xampp/apache/conf/ and open/edit "httpd.conf" file.
then search for line "Listen" (should be line number 120).
should look like that
#Listen 12.34.56.78:80
Listen 80
now change your port to the value you want to use for.
hope this help you ...
kr