Never fought that computer can restart cause of a map. Check for memory leaks in triggers, maybe his computer is too lame for it, or your map got huge leaks, errors or something. To avoid those leaks, you can use Custom Script. Check it in some tutorials if you don't know anything about it. Also, you can try reducing quality for warcraft 3 while playing it. I just asked my brother about it, he's a programmer, and he said that if the map requires good pc, it may cause a restart for not so good pcs =D