About 3 weeks ago I brewed my very first beer, a simple lager. I checked on the beer after 1 week of fermentation and now again after a bit over 3 weeks. At both times the density of the beer didn't really change. I think that no fermentation took place but I am not sure how to tell. Here is a photo of the beer http://imgur.com/okkHRnF, is this green edge above the beer normal?
I used about 7g of dry Safbrew T-58 yeast for roughly 5l and I still have about 6g left. The temperature of the room is about 15-19 degrees and it's quite dark.
Can I still activate the yeast or should I add some yeast? Is there any way to save the beer?