Assuming this is a *nix server of some sort, the user "nobody" is often used for services such as apache, mysql, etc. So you need to find out what process is running as "nobody" that is taking up a lot of system resources. Then figure out why that process or processes are taking up a lot of the system resources.
You could try logging into the server via ssh and type "ps aux" to see a complete listing of processes currently running. "top" might also help too.