Have you tried a different power lead and plugging into a different socket?

As a user community we have no way of knowing, but it doesn’t seem too promising. Contact Sonos and see what they can suggest. 

Sub 3/4? Not sure what you mean, is it a Sub gen 3 or did you get one of the new gen 4s which I thought hadn't shipped to users yet. Possibly the Sub Mini?

In any case remove the power cord from the Sub (not the wall) and reinsert it making sure it is fully seated.

When you first plug it in does the light do anything?

It's a Gen 2 Sub actually.  I'll have to call Sonos and hopefully get the 30% discount. I reseated the plug, changed wall plugs. It will not power up at all.