I don't think this is the long in password is it? like the password to log in?
This sounds to me like a BIOS password. heres how to get rid of it.

Open the computer's case and look for a battery that looks something like this



then carefully remove the battery and leave it out for about a minute then you can put it back in and try to boot the computer, and it should no longer ask you for the password.

This little battery helps to remember the computer the BIOS password so when you take it out the computer literally forgets it and it doesn't ask for it anymore.

if this is your first time opening up a computer take a look at this
INSIDE A COMPUTER

youtube video about this
YouTube - Bypass/Remove/Reset the BIOS Password