How do I open the top of a locomotive if my screw is stripped?
drill the rest of the screw out. :)
If the screw is other than a straight slot type, it is probably hardened. Trying to drill it out with an electric drill will likely cause it to over heat and melt the plastic around it. This may solve your problem but equally likely, it may destroy the shell you are trying to remove.
You did not mention if the problem screw has its slot stripped out or if the thread where it threads into the plastic is stripped. If the former, a better solution is to use a screw extractor in a reversible drill running backwards. But if it is the threads that are stripped, then turning the screw while pulling the shell off is more likely to do the job.
To avoid this problem in the future, use a screw driver that is an exact fit in the screw's slot. Then turn the screw in very slightly (1/8 to 1/16 of a turn) before backing it out. If the screw jams as it is being backed out, run it back in again and start over. The screws that give trouble are usually the self tapping ones that have a lengthwise slot that is supposed to pick up the shavings when it taps its hole. When you try to back the screw out, these shavings often bind, trapping the screw in place.