since bios upgrade, cannot set correct cpu/system speeds

[mannock]

i've flashed the latest bios for my m/board to enable installation of the fastest cpu my board will support. board is asus a7v266 and the old cpu was athlon 1.4 with system/pci set to 133/33 . now i have the correct bios version installed, and the new cpu athlon 2200xp but in the bios my choice of cpu speeds is manual, 2000, and 2666 even though the cpu is supposed to run at 1800. so if i set the system/pci to 133/33 and the multiplier to 13.5 it won't boot until i switch off then it runs in safe mode (the bios) saying the cause is 'improper cpu speed'
the only way it will boot into windows is to set it to 100/33 with a multiplier of 20 to give a cpu speed of 2000. seems illogical to me. i've looked hard at the amd and asus sites but can see no clues to what i am doing wrong. any ideas anyone?

[edwin]

clear CMOS

[mannock]

ok, i've done that. followed the m/board handbook instructions to the letter. still the same though. insists on calling my new cpu a 2000mh model instead of 1800. i wouldn't mind that, but i have lost more than i gained because it won't allow the system to run at 133.
i've even tried setting the multplier much lower but it wont boot up unless the system speed is at 100/33

[Denniss]

Either incompatible CPU or CPU is damaged somehow or some thermal paste has leaked onto some of the CPU L-Bridges( used for CPU konfiguration) and generated a short-circuit there delivering a wrong multiplier information to your board