Syntax errors in the config file seem to cause problems. I found what the problem was by going to the directory and excuting this from the command line.
httpd -e info
This gave me the error
Syntax error on line 156 of D:/.../Apache Software Foundation/Apache2.2/conf/httpd.conf:
Invalid command 'PHPIniDir', perhaps misspelled or defined by a module not included in the server configuration