If technology ceased to exist today, there would certainly be a massive die-off. Farmers would not have the ability, and possibly not the motivation to feed all of the newly-useless urban dwellers. Even if it would be possible for low-tech farming to feed everybody, it would be impossible to retool and retrain millions of people in time to plant this year. California would get it the worst. How would they even get across the desert and mountains to places where food is grown without irrigation?
How much useful electricity can you get from a donkey walking round in a circle driving a generator instead of milling flour?
Cut ahead a few years, we can avoid the effort of roads entirely if we brush the ground flat and pick hovercraft and hot air balloons for longer distance matter movement.
Machine tools are the foundation of just about everything, but there's a lot more to do once you can produce and shape metal. Chemical production is a big task once you have the handling of basic materials out of the way, and energy is important right from the start (electricity!). You'd have to have easy access to clean, and hot water to maintain good hygiene and a decent standard of living, which is important for morale. Which questions do we consider - just the technology part, or the kinds of social precautions you would have to take? A struggle for resources causes all sorts of difficulties. How would the economy work? There's no way to maintain governments like those we have today when there are no means for fast communication.
What is the easiest way to bootstrap technology from scratch? It would probably be a lot easier in temperate climates where food is abundant; in many parts of the world too much effort would have to be spent on just staying alive. The focus would have to be on tools right from the start: gather resources to build stuff and then use your new gear to build more stuff. Even if everybody knew exactly where we were going, it would take decades at the minimum. There is just so much to do, and so much of our technology depend on things we have developed already.
We could write books about this stuff. You could probably dedicate whole academic careers to the question, especially if you really want to try out the practical aspect. I'm disappointed about most of the posts on this story, there is so much interesting stuff to explore here.