My WordPress blog is hosted on a shared webserver on Hostgator. I've been having 500 Internal Server Errors the last couple of days. I haven't installed any new plugins since the errors started showing up.
I contacted tech support a few times but never got a succesful answer. The webhost has a process limit of 25. At times the process limit is reached, so the websites on that server go down. When looking at the process console, I see the process that's been spawning a lot is php serving the index.php file of my blog.
When I first contacted support, they told me it could be due to a large traffic increase on my site. But I have no reasons to think the traffic might have increased that much in a day. Checking Analytics (although most request must be getting lost due to the errors), I notice there hasn't been any important increase on traffic. Besides the site has been through some "Slashdot effects" before going to four or five times the daily hits average without any issues.
Another support guy told me to switch the WP-Super Cache plugin for W3 Total Cache, since that's the one Hostgator recommends. This didn't change anything either. I tried deactivating and uninstalling both, then checking with Hyper Cache, and I never found different results.
When changing WP-DEBUG to true, all I see are some warnings from All In One Seo Pack and this other plugin.
All of the tech supports told me there was a plugin that was causing this. So I disabled them all and started trying and enabling one by one. The thing is, I still haven't been able to figure out which plugin (if that's the issue) is causing the trouble. In conclusion, they haven't been of much help.
What are my options to debug and find out where the problem is? EDIT: My active plugins: Akismet, All In One SEO Pack, Dagon Design Sitemap Generator, FastFast Secure Contact Form, Google XML Sitemaps, Laconica Tools, List Category Posts, NextGEN Gallery, RubyConf Uruguay Ribbon, Smooth Slider, Subpage Listing, Subscribe to Comments Reloaded, UserAgent Spy, W3 Total Cache, WP-PageNavi, WP-Syntax.