Zuzu why do you have to change password each time? Does your password stop working or something? That would have to do with the PsychCentral site and not your computer, but I can't imagine that happening.
If it is your spy prevention software that is deleting your cookies, it might be easiest to let it do so and just log in again once it is done.
Can you describe what happens that leads you to have to change your password when this happens?