This is a very daft problem here, When I shut down my PC and switch it off on the socket sometimes its causing it to trip the switch in the house, I have a surge protection socket I wonder if that is the course of the problem??
Move the PC and see if it still does it or use another extension socket to test. I had a similar problem last year where a loose wire in a plug when high drain items were turned on would trip the house. Took about 3 months to find the fault!