From what I'm guessing, you cleared your CMOS.
When that is done, the motherboard will default the CPU speed to a lower FSB or to the lowest possible clock frequency it supports, and usually at POST the message "Error: CPU unworkable, Please check setup" will show up, and from there, the settings can be changed to correct the CPU speed (by selecting the correct frequency and multiplier). Once that done and the motherboard verifies the information is correct, those options probably will not appear again unless you clear the CMOS (usually by setting the jumper to a different location).
The Coppermine/Tualatin PIII and P4 Celerons are multiplier locked, so unless your motherboard has an option for adjusting the FSB, then you may have some luck.
But then again, there's always CPUFSB