Firstly, you bought a storage building full of stuff?
Secondly, I am surprised that someone left a laptop there. Maybe it was by accident?
Generally, this should be fine. Do you know what operating system the computer has on it? In XP, it is really easy to bypass a user account password. If it is a BIOS password, it'll be quite a bit harder, but I'm sure there is a way to do it.
If you know what the OS is, post back.
BTW, if you didn't know, a BIOS password is one on a black screen (generally), with a blue box in the middle reading "Password: __________" or something similar.