Okay, this is how horror/stalker/slasher movies start. Phsyco drops laptop at pawn shop, J. Random Netuser picks up laptop, and one of the following happens:
1. Laptop explodes while J.R.N. excitedly boots laptop in parking lot, firey death.
2. Laptop electrocutes J.R.N., he dies in a convulsive seisure.
3. Laptop works great, while SkyNet runs in the background getting smarter and smarter.
4. Laptop works, J.R.N. enjoys browsing Tom's Hardware while watching TV from the couch, laptop overheats and burns certain "family jewels".
5. Laptop is in fact stolen and the whole thing is a setup.
6. Laptop webcam is remotely activated, J.R.N. is blackmailed for who-knows-what.
7. ...
8. Profit
I don't like the sound of it at all, but then again I don't usually trust a pawn shop for anything but secondhand tools or golf clubs. But hey, if you got a great deal and you want to keep it, go ahead! Tell us the model number and where this password is, (BIOS/Operating system/whatever) and we'll help you as best we can.