For me Punk was (is) more about attitude than the music, it was a collective feeling people had that things could change (for the better), it also broke down racism to some degree, gave people the idea and motivation... anyone can do it! It had spin-offs in fashion, art etc that we still see today, that all has to be a positive thing.
As has been said and I agree it's pretty hard to label the early punk music as a certain type of sound but you can certainly see an attitude.. from the Jam to the Pistols, Clash, Damned etc.
I'd say the youth gave it a pretty good go from 76-80.. for me it all got old hat very quickly after that once Punk became a uniform and simply relied on how fast you could play.