All I recall is the protagonists may have been kids (perhaps a boy and a girl). I seem to recall them either crash landing on an unknown planet, and constantly trying to outrun large spherical (probably red coloured) sentinels that were trying to kill them. I think the sentinels were Cyclops with lasers that were coming out of their eyes.
In the quest understand the history and why they were being hunted they discover a long lost underground city, with noone alive. And culminates in finding a room / hall with a weapon (looked like a rocket launcher or something). Leading up to a weapon was the dead body whose last moments may have been trying to reach the weapon.
Anyway they get the weapon, but the video tape ended.... I have been hunting for this for decades.... Please help.