Dedicated Linux hosting server keeps crashing

I need someone VERY experienced in Linux, using SSH commands and Plesk to help. My server crashes because it's out of memory. Something is eating up the RAM and I think it's MySQL. There must be a malicious script running on a site. I need you to quickly identify the culprit and solve the problem. I did the top command and MySQL was close to 100% of CPU. I also ran the command to see what IPs were connected to the server and a few were spam servers. Every time I executed "iptables -A INPUT -s IP-ADDRESS -j DROP" a new spammer IP would be connected. In the past MySQL has crashed at least once a month and the server was fine after a reboot. That's not the case now. My budget is very small and I can't pay more than the budget so if you feel you're not proficient enough to quickly and easily fix this, please don't bid. Also don't bid over the budget. This should be an easy fix for someone experienced. Also an unrelated problem....after I upgraded plesk, some users have been unable to send emails with attachments to the other emails on the same domain. Also if there is a fwd set, the server refused to fwd the email to an email outside the server. [login to view URL] dedicated server CentOS CPU: Opteron 1216 HE CPU Details: 2 x 2.4 GHz RAM: 2 GB RAM Hard Disks: 2 x 250 GB (Software RAID 1) Plesk 12