CSRSS.exe going ape
This was something that was really weird. Seemed that our intranet server was going crazy! When we remoted into it the screen kept flicking and looking at task manager, the csrss.exe process was doing some tremendous reads from the disk.
Turned out that someone left the keyboard plugged into the server and jammed it back into the rack. As a result one of the keys got stuck. The constant pressing of the key is what was causing the problem.
Another day in tech support