As previously mentioned above in the comments - and tested out myself:
This error is rather ambiguous. Therefore, you should check the error.log located at \xampp\apache\logs
When I had this issue, it was because Skype was already listening on port 80 & 445. I was able to get around this by exiting Skype, starting the Apache service, and then restarting Skype. You can check the current port listeners by opening a command prompt and typing Netstat -a
It is also recommended to have User Account Control OFF as it may block some features built into xxamp.
Prior to this though, I had an issue after I modified my Apache httpd.conf file. Reverting those changes (or reinstalling in the user's case) will resolve that issue.