Well that means you've got a bios password set.
If the pc was supplied by a computer manufacturer and you think they have set it, I advised you speak to them.
If you have no support due to self build etc? and either have forgotten the pwd or someone else set it. Then you can clear the cmos, taken motherboard battery out for 2hours or find relevant jumper.
I would not recommend going in the pc if you have warranty, as it could be invalidated.