It sounds a lot like the Stirling trilogies "Island on the Sea of Time" and the "Dies the Fire". Both outstanding sets of books. They both start at the same point, 1998, a blinding flash of light occurs, and things go to hell. In Dies the Fire, everything technological dies right along with the flash of light, electricity, explosive chemical reactions, etc, sending the modern world back to the technology level of the middle ages. In the "Island on the Sea of Time" the flash occurs, and the Island of Nantucket is completely cut off from the main land (by about 3,000 years). In both sets of novels the people have to deal with the sudden dramatic upheavals. I think it makes for a really neat story, and it definitely puts Jericho on my must watch list.