You're not alone with that behaviour on an Asus board.
 
Same thing happens with a PIII 550 CuMine being dropped to 366 on a brand new P3b-F with the latest bios. Everything is set to auto and no overclocking, plenty of cooling.
 
Starting to lose some faith in Asus these days.
 
Say what you want about AOpen, but I've been using my AX6BC for over two years now, 4 bios updates and dropped in processors from PII-266 all the way to PIII-800 with no problems, full ACPI support in all Win2k server family and rock steady performance.
 
The only beef I have is overclocking is a little weak, but I think the trade off in stability more than makes up for it.

updated the bios to 1002 and now it works fine..still have some probs with the oc..but im on that mutha

This happens to me only when it has an error on boot(see also my pressing the power button because I hit restart instead of shut down). If you go into your bios, it will usually say something about your CPU in red. Dismiss it, and restart, and it's back to normal

I've had the same action happen twice when I reset the motherboard before it finished POSTing. Basically the CUSL2 assumed that an error had happened, and it wants you to correct possible clock issues first.
 
Just dimiss it, and you should be ok...
 
HTH.
 
------------------
J. Byron Todd
Computer Consultant
byron@toddcomp.com
Todd Computer Solutions