I don't really understand your question. You say it was green 6 weeks ago ? do you mean it had leaves on ? Wisterias are deciduous and drop their leaves every autumn. if yours has just dropped its leaves then i can only presume it's either under glass or you live in another country (which would be hand to know as this is a ".co.uk" site.)
One test to see if any plant is still alive is called the thumbnail test. Using your thumbnail, scrap away a small section of bark from the stems in question. If there's any green wood underneath, the plant is alive. If it's brown, chances are it's dead.
Now this test will only work for the section your scraping....eg that bit might be dead but the rest of the plant is alive so check several areas.