i have a few questions - help needed please! (Spoilers inside)

1: We don't know, but can be assumed the robot moved the body.

2: The robots were suppost to check all employee badges, if they check out the robots don't do anything.

3: The computer is not on the roof, but that is a transformer, due to the lightning stike it shorted out the computers controlling the robots.

4: No clue

5: My guess is the lightning strike did something to the system, or the robots turned off all emergency systems

6: They are only used at night, they are up there because of where else would you keep them

7: The robots were controlling the temp of the mall, I think the girls even said it was getting hotter when they were in the vents

8: The laser hit a mirror and the redirected it back at the robot

9: Only thing I can think of is to open doors

10: The robot crashed into the shelf knocking the spiders and snakes to the ground.

1 - What happened to the body of the first technician? we see him being killed but nothing after that - what has happened to him by the time the second technician enters the room and doesn't see him?

The robot hid/disposed of the body.

2 - Given the teens employed in the mall will know about the robots tasering intruders, why do they still have the party knowing the robots will detect them?

They were going to leave before the mall was locked up for the night and the robots went on duty, but the robots went online early due to the electrical surge from the lighting strike. This is how Dick Miller (the janitor) got killed, because he was still mopping up when the robots went into service earlier than expected.

3 - Why is the computer controlling the robots on the roof?

There are no robots on the roof. There is a satellite/power feed on the roof which presumably connects to the computer which connects to the robots.

4: What is the difference between the shorter film version (75 mins) and the longer one (90 mins)?

There are at least two different versions of the movie. The TV cut has some extra footage, such as a small homage to Attack of the Crab Monsters, extended scenes of Ferdy and Allison watching TV, some aerial shots, and an extension of one of the Ferdy/Allison scenes.

5 - The teens and robots between them cause an incredible amount of damage, including fires and smoke. Why aren't the fire alarm and sprinklers therefore set off?

These are all controlled by the computer system which the robots apparently gained control of when they went batsh*t crazy.

6 - if the robots are meant to patrol the floors, then why are they kept in the technicians' room instead and only get out by killing them?

Storage...they are only meant to patrol when the mall is closed.

7 - why don't the gang go back up into the airvents when they are together again as they're safe there?

Because it's hot as *beep* up there, as detailed in the scene when the women were crawling around in the ducts..

8 - What made the second robot start electrocuting itself? It just suddenly seemed to happen!

It blasted a mirror which caused a ricochet back unto itself.

9 - We learn from the scientist at the start that the robots are only equipped to fire tasers and sleep darts. So why do the robots suddenly have those pincer thingies to cut peoples' throats?

The 'pincer thingies' are armatures which allow the robots to grasp things like door knobs and such. The fact they were subsequently used as weapons later was primarily due to the messed up programming as a result of the power surge.

10: When the last survivor is hiding under a shelf in a store, suddenly she has snakes and spiders crawling over her. Where did they come from? Even if it is a pet store, don't tell me they just let their livestock run around free

The robot plowed through the pet store, knocking over display cases causing the snakes and spiders to be set free.

You didn't pay much attention, did you?