I'm working on an idea for a story. It takes place in the somewhat distant future, say 200-300 years. Some time between now and then, an event occurs which causes all computers to simultaneously fail. This event is NOT the result of terrorism or malice, it is more or less, an accident. (specifically it is caused by a well-intentioned AI that is less powerful than expected and cannot withstand the strain of all the tasks it is given)
For the purposes of the story, I want this event to greatly reduce the population of Earth, and also effectively put an end to most or all major cities. I don't want it to threaten extinction, just reduce the number of humans by some large percentage (a lot of leeway here).
My problem is, I'm not sure what we could rely on so heavily that would cause this much destruction. I imagine that the following thing would happen all nearly simultaneously:
- Complete failure of power grid
- Meltdown of all nuclear power plants
- High-tech farming equipment no longer functions or malfunctions
- Traffic lights, streetlights, trains, subways all either fail or malfunction
How much actual damage would these failures do? Would these things alone be enough? What other consequences could there be?
EDIT for clarity: I am not looking for something that would cause technology to fail, I am looking for the effects of loss of all technology and how it would reduce the human population.