back window is not working anymore

I have a GMC 2005 Envoy. The window dividing the passenger seat from the rear does not work anymore. What can I do to fix this without much costs? Is there some items I can check before going to a repair shop? Also, I was just told that my brake light is out. Window does not function anymore. Separates passenger compartment from the storage/bed compartment. Would like to know if at all possible, would a fuse change fix the problem before going to a mechanic. Also, would like to replace the right-brake light but not sure on how to remove cover. Please advise.