"Waiting for *server*..." forever.

[eluser]simshaun[/eluser]
What makes me come to that conclusion is this:

I’ve had a look at the Apache logs, and it looks like a 404 error looking for /internal_error.html occurs every time this problem happens. There’s also the occasional “Premature end of script headers: php5.cgi”

Out of curiosity, have you tried removing the htaccess file and testing from there?
Its the only thing I know of in CI that will cause Internal Server Errors.

If it still does it after removing the htaccess file, then I can almost guarantee its a problem with your server.