How did someone put a BIOS password on your laptop?
Do you recall lending it to anyone?
Do you know of anyone who would pull as mean practical joke on you who has easy access to your laptop?
Anyway, if whoever put that password on your laptop does not come forward, then you need to contact Sony support and provide some type of proof that you are the original owner. You may be required to send the laptop to a service center.
If you can get this issue resolved, then my advice is to put a BIOS password on your laptop so that no one else can pull this stunt on you... Just don't forget your own BIOS password though....