1. Have you tried using the newer control panel (xampp-control-3-beta.exe)? (There is an update available here: viewtopic.php?f=16&t=48932
2. Are you sure Ports 80 and 443 are not being used by anything on your system? (Skype, VMWare, Windows services such as World Wide Publishing Service, and other applications have been known to use and block those ports. These must be free for Apache to start. You can check it with the Netstat button in the Version 3 Control Panel mentioned above.)
3. Did you install with the Installer for the ZIP file? (The installer has been known to cause problems with installations)
4. Did you install XAMPP to a location where the path to the folder does not contain any spaces or special characters? (Ex: The Program Files folder would cause problems)
5. If you installed XAMPP to the non-default location with the ZIP installation, did you run setup_xampp.bat?