Lock multipliers question

Hello there, I am a newbie at the overclocking business and I want to know what happens if I change the multiplier of my cpu to something else than the stock one, what happens if it is locked, wont the frequency change and just stay there? or wont it turn on.

I cant believe nobody is answering this...

Different motherboards will react differently, some will just POST with the stock multiplier, and the speed won't change. Others will not post at all. clearing the CMOS will solve that.
But if its unlocked the speed will change.