I have had this problem before and I'm sure most Xampp users have as well. When you start Xampp control panel and click start on Apache and MySql, sometimes Apache stops after running for a few seconds. Why? This could be caused by something you may have opened on your computer. I recently had this problem and wondered why my localhost was loading up with a blank page. I was almost ready to delete all of my files I have set up. After a few minutes of that, I checked my Xampp control panel to see that Apache wasn't running. I started to check what was running on my computer. At that time, all I had running was my anti-virus of course, Xampp and Myspace IM. I exited out of Myspace IM and Apache stayed running. Certain programs such as Myspace IM keep Apache from running.
I thought I would share this with the Xampp community in case they had a similar problem.