Whoa - wait a minute.
Okay, so if civilization failed, and for whatever reason all factories in the world were destroyed, why are we unable to do anything? Why are we in the stone age, if not worse, again?
Seriously, we made those machines. There are people who work at those factories, that's job is to know about the machine. They can tell you what each and every pipe and valve and glitchit is for. These whizgiz's are, yes, made by machine - but not because we don't know how to make them. It's just easier and less costly.
If the factories all went ka-boom, we wouldn't have to start at step one. We start from the last model, and downgrade whatever we can't create with the materials avaliable until we get something we can make. And we advance from there.
And besides, advancements don't come from civilization - civilization comes from advancements. Advancements don't dissapear, they can become lost - but nowadays it's very difficult to see someone who isn't capable of building a crank, lever, or pully system. We live several decades longer, we are much healthier, and most importantly many of us are educated. I can read and write, and understand 3 languages - plus I can count from 1 to 1,000. And while most common folk would know what "1" is, and that "1,000" is big, I'm sure most of common folk in ages mentioned wouldn't be able to do so.
Military men and women can count, often can read - but not always, and will most likely have some understanding, even if crude, of a forign language. Same goes, in general, to higher and more worked political and merchant based groups as well, back in the day. And I pretty much summed up half of, at least, the United States.
Bakers can still bake - they may not be able to know how to make the grain and flour etc... but a farmer can (and not all of this is done by machines). We simply downgrade our cars to horse drawn buggies again - or just drive the cars we have... - and team up the baker and the farmer. We take the guy who spent too many hours learning up on ancient war weapons and chainmail fantasies, and we put them with someone who works with metal. We take a carpenter and... well... there's really no one to team them up with. They can build us our factories, the metal dude could smith the machines, the baker and farmer can feed everyone, and I'll build the rope and pully systems that aline the machines back together.
Civilization's already fallen several times. In each region that had a "great" and "golden age" practically. Rome fell how many times? And each time heralded a new "dark day", but they didn't have to start from step one. Instead they carried on from where they left off.
All the machines can go. We still have the plans and knowledge to remake them. Unless all the educated people and the machines go, there's really nothing to it.