2. If sirens and lights went off when you tried to open the hatch, then the ship is still in space. You can't open the hatch while the ship is in space, of course. Don't go on to the next hint until the ship has landed.
3. Do you remember an announcement when the Heart of Gold landed on Magrathea?
4. Eddie (the shipboard computer) is jamming the hatch to prevent anyone from leaving the ship until he's checked to make sure the environment is safe.
5. If you wait the 17 years such a check will take, you'll probably die of boredom.
6. You'll have to figure out how to override Eddie's wishes by fixing the hatchway mechanism in the Access Space.