Jojopapar;
If its a KT133, not a KT133a, it probably will not boot at 133, even though there is a bios setting for it. It just never ran well above 110 mhz or so.
Options:
Replace the board with a more current KT133a, KT266, SIS735, KT266a or Nforce board.
Replace your processor with one designed for 100 mhz bus.
Unlock your processor with the "pencil trick". Set the multiplier to 12x.
Live with 900 Mhz.
Hope this helps;
Doug