Wind and hydro-electric production are implamentable without signifigant prerequsite manufacturing. Yes, they are more efficient with high-tech equipment; but if the more basic generators created an "island of power" were more high-tech manufacturing could be performed you could easily kick-start back to a modern system.
Use the low-tech hydro-power for a biofuel plant (power digging or recycling equipment) and the production of better hydro-power generators (or solar-power, etc).
Don't get me wrong: there are some massive hurdles to overcome; but for key infrastructure we could replace oil even in a boot-strap society.
Note: the whole supply-chain is far more complex than most people realize. The dark ages weren't so much about lost knowledge as lost infrastructure. In a "new society", getting the needed resources to the needed location would, I think, be the biggest single problem. You can't just build a microprocessor plant out of the blue; it requires hundreds of other systems to make it go.
The biggest issues on a "global restart" are "population" and "infrastructure / government"... at least in terms of moving back to an industrial society.