Error 500 on all php pages

Hi folks,

I'm not sure what happened to my webserver - I wasn't doing anything unusual with it, and all of a sudden every php page I bring up throws an error 500 - even phpinfo.php.

I'm looking at error_log, and I see a lot of this:

[Sun Mar 22 22:00:38 2015] [error] [client 66.249.67.31] Premature end of script headers: phpinfo.php

html pages render fine, and I can use WHM without issue. I've been frantically googling, and found some bits about suexec_log reaching 2GB that might cause this. I rotated the log, it's writing to it again, but still no dice. I also restarted apache, restarted my host, and tried enabling and disabling suexec. I'm completely stumped.

Any insight would really be appreciated, as my clients are all dead in the water and I'm totally out of ideas.

Edit:
Server Version: Apache/2.2.29 (Unix) mod_ssl/2.2.29 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4

 

Couldn't tell you what I did - honestly I was just fiddling with a gallery on a vBulletin forum.

Here's a folder list. I'm 99% sure it's permissions based but I've no idea what they should be. I'm testing two domains. One works now, the other doesn't, so I don't think it's php.ini.

Here's one that works (with the actual folder name changed)

-rw-r--r-- 1 user1 user1 168 Mar 22 22:23 /home/user1/public_html/phpinfo.php

Here's one that doesn't:

-rwxr-xr-x 1 user2 user2 168 Mar 22 22:27 /home/user2/public_html/phpinfo.php

I'm going back and forth trying different permissions (755/644/777) but honestly I don't know what these should even be.