Difficult to say without knowing the model...
It may be that the lock out is temporary, in which case all will probably be well soon.
Alternatively, it may be that you have to remove the battery from motherboard until the BIOS has reverted to its factory settings. Again, there may be a way of causing this without removing the motherboard battery.
The best thing to do would be to consult the manual. It's important to remember, though, that this lock out is designed to prevent unauthorised access to the machine e.g. it it had been stolen, so it's not supposed to be easy to bypass otherwise there would be little point in having it in the first place..