firstly thanks for responding.
but it's too bad that I can't remember all details needed.
in other words, it just happened when I use it and then I only find it read as 1,86ghz on the next booting.
since that incident, I haven't made any change on my cpu except replacing old memory and display adapter.
it's still doing the same old way to boot
I've visited bios check many times but when I forced to make my processor to be detected as 2,66ghz (by changing one of the power options) the cpu doesn't start at all.
it's just beeping once and then restart but everything turns back to 1,86ghz detection.
I'm still wondering how could it be that way, even some technician said this is their first case
what a mess.. haha