With versions 5.4 and onward, certain php.ini directives can cause your site to no longer load.
Make sure all references to the following are removed from your php.ini:
allow_call_time_pass_reference
magic_quotes_gpc
You can place a semi-colon in front of those lines to preserve the old values in case you need them for future reference.
;allow_call_time_pass_reference
;magic_quotes_gpc