Something else on your PC server is probably using port 80.
A Test would be to make apache listen on another port, try 8080.
Look for the line Listen 80 in httpd.conf and change to Listen 8080. Then Restart All Services from wampmanager.
If all goes green then something is using port 80, possibly IIS, but could be a number of things. You will just have to search for the other process.
Look here for how to do that
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