It sounds like the 2.4ghz processor he put in is a Pentium 4 2.4C processor. The C indicates that it is expecting a 200mhz bus (800 marketed number), something the FS51 can't do. The FS51 is limited to a 133mhz bus (533 marketed), or 150 overclocked.

(Grr, proxy at work died. SSH tunnel to the rescue)