Windows 2000 could not start because the following file is missing or corrupt:\WINNT\SYSTEM32\CONFIG\SYSTEMced

Does anyone know the cause of this, the microsoft knowledgebase told me "The System hive in the registry is damaged or missing."
I am running:

Windows 2000 Professional SP2
AMD 1.2GHZ
Abit KT7-Raid
ATI 64mb Radeon
128 mb ram

The only thing I do to the machine is change the bus to 101 when I game a little, then move it back when I am done.