This is one of the most common errors faced by Apache users.
So many sites/Forum must have suggested ways to correct this errors and it still doesn't work.
I am going to show you one simple way to detect the cause of this shut-down and error and how to fix it.
Generally, people believe it is because of other applications on your system using the same port e.g Skype using port 80, and conflicting with your Apache port. you don't necessarily have to uninstall your applications of change your port no from your httpd.conf file.

Now lets get down to business.

One of the major causes of this error is when your're trying to change/configure your vhost (i.e httpd-vhosts.conf file) or host (hosts file) name, when working on a project. once there is a mistake in any of the file, it will affect your apache. So, be careful

To see what is causing this error and correct this,
open your Xamp
click on "shell" on the right (it has this little command line icon)
when the Xamp command line opens, ........type ap and press tab twice
this will change to apache_start.bat
press enter
This will display the error message, and the line number where it is found, and the file where this error is located etc.
locate the file and correct the error.
Restart your Apache and everything will work fine