This has probably been gone over but I think my kefir might be dead. I left it on the counter for a couple of weeks without changing it. There was a few grains that had turned into strands of mucous. The liquid tasted fermented but very sweet. I would have thought that after a couple weeks the sugar would have been gone. The grains have turned more of a brown color.

They probably are dead.  One thing you can do is to put some plastic wrap over the mouth of the jar and apply a rubber band to hold it on.  If the grains are alive and fermenting gas will develop bulging the plastic.