My wife took my clk to work this morning. After she came home she went to leave in the car. The car will do nothing. Power locks don't work. Power seats no go. Key will not turn in ignition. I tried my spare key -no help. When I opened the door with the emergency key the alarm went off. For quite a while. I finally opened the trunk with the key and unhooked negative side of battery. I noticed the nev cable was pretty loose. I tightened but it didn't help. Dead battery? Other ideas? Thanks.