Re: If you were on the Enterprise D, what would you do?
The original post doesn't specify which Enterprise. In any case, something must be amiss if the turbolift grants a civilian security access to the bridge and other restricted areas. First step would be to see if anyone can be contacted on the planet. If friendly, ask for or offer assistance. If hostile, order the computer to set course for the nearest habitable starbase, after a full orbital phaser barrage at hostile's coordinates.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)