how can i disable power button?
You'll need hardware support for that. Or nice "there, I fixed it!" tape. A longer press on this button will inevitably power down the PC very roughly, no matter what OS you run on it or what program you try to have that prevent it.
For just ignoring the simple "hits" on it, go to your power settings and let it do nothing on pressing it:
Above screenshot is in KDE, but similar settings should be available in your Desktop Environment too (e.g. Unity, GNOME, ...) See this answer for Unity.
Locking keyboard, mouse
Have you tried setting a password to your screensaver? Or set up a custom shortcut to activate the screen locker (default Ctrl+Alt+L)?
eject -i on
to lock the optical drive :)