Most of those CPUs that I've seen are only 66FSB, if I recall. I have two Celeron Slot1 CPUs and they both are 66Mhz. What is the CPU model (ex. SL27Z). Do you have 100Mhz memory installed? You may be trying to overclock, which might require some wizardry (and 100Mhz memory) to work.
This quip from the manual seems to know:
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Assuming this is the correct manual. It's always nice to see your actual board and setup, to make sure we're all looking at the correct board.
It'll be way easier to acquire a Pentium 2 or 3 100FSB than to try and force 100FSB. Kinda high-level overclocking. Like trying to overclock a coppermine. Not really do-able.
Main Loadout (daily drivers):
Intel TE430VX, Pentium Sy022 (133), Cirrus Logic 5440, SB16 CT1740
ECS K7S5A, A-XP1600+, MSI R9550
ASUS M2N-E, A64X2-4600+, PNY GTX670, SB X-Fi Elite Pro
MSI Z690, Intel 12900K, MSI RTX3090, SB AE-7