If you bought the laptop second hand, talk to the seller. If you are the original owner, you can phone dell with proof of purchase, but if you bought it second hand and the other owner was not the original... there isn't much you can do... there are some people online who offer unlocking services, but it can be costly. The services usually involve wiping out and reflashing the BIOS, which also has no guarantee.
A company I worked for in the past gave away a lot of off-lease machines and many of them were locked in the way from IBM and no one had the passwords anymore. Most of them were junked, and the ones with the best hardware were sent out to be reflashed.