Found this on the MSI site for your motherboard:
* When FSB setting 166MHz the memroy only can
running at DDR333 mode.
Nice spelling MSI have.
More importantly, this means you need PC2700 (DDR 333Mhz) RAM to operate with processors running with the FSB at 166Mhz - which may be the problem you're hitting?
I'm not sure about this - I'm not feeling very well and have a bastard of a headache, so I'm not up to much traipsing around google.
Knowing what processor you have would help. AMD processors start using 166Mhz FSBs (ie. 333Mhz when doubled up) at the XP2700 afaik.