I had the problem today. When i started Apache from Xampp control panel, CPU usage became 100%. Nothing changed after apache restart and PC restart. Same.. - 100%.
So to understand what is happening you need to
1. go to: C:\xampp\apache\logs
2. open access.log with text editor
if file is too big to open ( bigger than 5 mb ) do this:
1. just delete access.log and error.log
2. start apache and stop it after it will start loading your CPU to 100%.
In access.log, you will be able to figure out what is happening with your apache ( httpd ).
In my situation was some kind of apache virus ( which affects my files with new scripts called webdav and webalizer ).
So if you have the folders in your xampp folder, that means you have same problem..
i solved it by this way:
1. -> Control Panel\Network and Internet\Network and Sharing Center
2. -> Windows Firewall
3. -> Allow programs to communicate through Windows Firewall
4. Removed Apache HTTP Server with checked under Public ( To do that press Change settings button on top )
5. Close everything.
It might not help you. So here is one more idea what you could do in the situation:
After finding out what IP requested execution of the script in part with error.log just Block it! Google for answer..