C2 Mercedes will not start, battery bought in Jan.what's the problem

There is too little information here to do any diagnosis. Please restate or Add a comment to this post of: what sounds do you hear or don't hear? Any smells, what do you see happening? When you put the key in the ignition do you see the dashboard lighting up telling you there is power? When you put the key in turn it a little but do not start it, do you hear a whine or shutter from under the rear of your vehicle? (that would be the fuel pump). When you turn the key do you smell anything? Do you hear the vehicle clicking or attempting to crank? Is it slow or fast? Loud or soft? Please give all the details you can, because your Mercedes is an internal combustion engine which has the battery basically only to help it start. There are over a hundred reasons why it may not. So if you could please all the information you can give will help narrow that number down.