Define "PC Security System Circuit for parallel port" please, that could mean many things. Are you looking for a genuine security solution, or just something you can show off to your friends? What do you want it to do, sound an alarm if your case is opened?
And please use some better grammar in your posts, it's easier to read and encourages people to actually respond. (Unless you aren't fluent in English, in which case I think you need to review your punctuation, capitalization, and spelling chapters
.)
Here's something I'm thinking of doing. This is hardly a circuit, and it definitely doesn't plug into the parallel port, but hook a key switch as from
this site in line with one of the wires from your power button. Now you have to turn on that switch for the power button to work. A momentary key switch on its own would be more elegant, but those switches are less common and more expensive.
But anyone who knows anything about breaking into computers would get around that fast, unless you have your case locked as well. It's mostly for the coolness factor that I would do it.