All of the sudden my website only showed a '500 Server Error' page. I found the problem - I had a large number of processes running, which seemed to 'freeze' my website. Once I forced them all to end with cpanel, everything was fine. However, every few minutes the problem returns. The two lines which constantly repeat in the process manager are:
/usr/bin/php index.php
and
/usr/bin/perl -w /usr/sbin/sendmail -t -i
If anyone has experience with this kind of problem, I'd really appreciate it!
I would presume that one of your PHP scripts is hanging due to sendmail, so the processes get zombified, and once your PHP process count hits a limit, you start getting Service Unavailable errors. Try pinpointing which script it is.
I have a really strong feeling it is a bot exploiting a hole. I temporarily removed the contact form from my site and instantly the bot isn't bugging me anymore... I'm going to look into it tomorrow to see what's going on. But thanks for the help once again DevNetwork users!!!