first off, the PC doesn't have a password as far as I know, you can just mess with it. The door has a password, but that one Alex told you before you entered. It was 65 76 69 88 which, as the hint suggests, is ALEX in ascii code.
I'm not an IT guy so don't quote me on this but in this context it's basically how a computer "writes" on the screen: every character you can type has number assigned to it A is 65, L is 76 and so on.
