Are you using XAMPP? When you click on Apache does the program seem to start and then magically stop? There are several apps that can actually setup little web server services that can interfere with running a webserver on port 80. In my travels these are the programs that seem to cause the most issues:
IIS can be installed without you knowing by certain applications. IIS is a webserver and uses port 80. When IIS runs you might notice when running a netstat command that PID:4 is running by system. To check if IIS is installed on your machine go check out your services. Look for “World Wide Web Publishing Service”. Stop the service and run Apache through the XAMPP control panel.
Look for anything that might be called IIS …. in the add remove programs as well as Microsoft’s Visual Web Developer. Remove both of those items and reboot the machine.
Teamviewer & Skype when running starts up a service on port 80 that can interfere with XAMP and cause Apache to start and then quickly stop again.
I’ve seen where VMWARE opens up port 443. Because Port 443 is also opened when XAMPP’s Apache opens up and can cause a similar issue.
Hope this helped you when Apache wouldn’t start.