One day when I try ot turn on my computer, there is dialog bar come out said the computer is locked only me (my name) or the ministrator can unlock it, under this is user name and password and that is highlight and could not type anything in. The problem is I never set any password in this computer and I am the only one use this computer, and even I could not turn off the computer, so only I can do is pull out the power let it run out the battery. So how can I unlock the computer? Thank you.