hello,
that screenshot indicates a problem with spamd (this is part of spamassin) to find the cause of a 500 internal server error ssh to your server and
Code:
su -
password:yourrootpassword
tail -f /usr/local/apache/logs/error_log
you could disable spamassin since it's quite resource heavy also your serverload is way to high time for some "finetuning" or the server won't run anymore for long...