What does it mean when I dreamed of changing my PC password. Is it a sign that i should or what?

Periodically changing your PC passWord is always a good idea. But that probably is not what the dream is about. Dreams work with symbols, so you need to think what your PC passWord might represent.

You are right to begin thinking in terms of safety issues. Your passWord lets you "into" your computer. What else do you have or use that lets people "into" your life? Your keys are an obvious possibility, as is the information you post on public sites like FaceBook. There are personnel files and medical files. Have you filled out job or loan applications lately, which might let others "into" your private information? You could continue thinking along these lines.

Another possibility is that your subconscious may have picked up subtle indicators that someone in real life is intruding where they should not be. Is there someone you have let into your life, or perhaps thinking about getting closer to, who may not be who you think they are? Your conscious self might not have seen something that your intuition noticed. So look again, think about it and be careful.