Apache appears to be running OK and when I go into the xampp control panel I can check phpinfo() and everything shows up just fine. When I try to open up any php files in my browser the page is blank.
Here is my Apache error log
[Wed Aug 29 07:07:19.160419 2012] [ssl:warn] [pid 280:tid 376] AH01873: Init: Session Cache is not configured [hint: SSLSessionCache]
[Wed Aug 29 07:07:19.768831 2012] [mpm_winnt:notice] [pid 280:tid 376] AH00455: Apache/2.4.2 (Win32) OpenSSL/1.0.1c PHP/5.4.4 configured -- resuming normal operations
[Wed Aug 29 07:07:19.768831 2012] [mpm_winnt:notice] [pid 280:tid 376] AH00456: Server built: May 13 2012 14:10:15
[Wed Aug 29 07:07:19.768831 2012] [core:notice] [pid 280:tid 376] AH00094: Command line: 'c:\\xampp\\apache\\bin\\httpd.exe -d C:/xampp/apache'
[Wed Aug 29 07:07:19.768831 2012] [mpm_winnt:notice] [pid 280:tid 376] AH00418: Parent: Created child process 424
[Wed Aug 29 07:07:20.673648 2012] [ssl:warn] [pid 424:tid 268] AH01873: Init: Session Cache is not configured [hint: SSLSessionCache]
[Wed Aug 29 07:07:20.767250 2012] [mpm_winnt:notice] [pid 424:tid 268] AH00354: Child: Starting 150 worker threads.
[Wed Aug 29 07:18:17.441000 2012] [mpm_winnt:notice] [pid 280:tid 376] AH00422: Parent: Received shutdown signal -- Shutting down the server.
[Wed Aug 29 07:19:34.371074 2012] [core:warn] [pid 1608:tid 376] AH00098: pid file C:/xampp/apache/logs/httpd.pid overwritten -- Unclean shutdown of previous Apache run?
[Wed Aug 29 07:19:35.104275 2012] [ssl:warn] [pid 1608:tid 376] AH01873: Init: Session Cache is not configured [hint: SSLSessionCache]
[Wed Aug 29 07:19:38.193080 2012] [mpm_winnt:notice] [pid 1608:tid 376] AH00455: Apache/2.4.2 (Win32) OpenSSL/1.0.1c PHP/5.4.4 configured -- resuming normal operations
[Wed Aug 29 07:19:38.224280 2012] [mpm_winnt:notice] [pid 1608:tid 376] AH00456: Server built: May 13 2012 14:10:15
[Wed Aug 29 07:19:38.224280 2012] [core:notice] [pid 1608:tid 376] AH00094: Command line: 'c:\\xampp\\apache\\bin\\httpd.exe -d C:/xampp/apache'
[Wed Aug 29 07:19:38.317881 2012] [mpm_winnt:notice] [pid 1608:tid 376] AH00418: Parent: Created child process 2812
[Wed Aug 29 07:19:40.221084 2012] [ssl:warn] [pid 2812:tid 268] AH01873: Init: Session Cache is not configured [hint: SSLSessionCache]
[Wed Aug 29 07:19:40.252284 2012] [mpm_winnt:notice] [pid 2812:tid 268] AH00354: Child: Starting 150 worker threads.
Are you using Windows 7
Windows 7 has webserver which uses Port 80
so apache might not be running.
Check if port 80 is being used
To change port no of Xampp apache check this link
Xampp server port