The main issue with ports is something using port 80, which 90% of the time in the past, it was Skype that was the culprit. Skype by default chooses port 80 and the workaround is simple ... shutdown Skype, start Apache, then re-launch Skype and Skype will choose a different port automatically.
The other issue could be with Windows Firewall blocking it, Windows User Account Control, etc., which it should alert you saying that an application is trying to access it and allow you to accept or deny it, depending on your settings. So if the first part doesn't work (Skype), then troubleshoot these two areas.
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