My car won't start, why? on 2002 Mercedes-Benz C240

last week my car wouldn,t start,i got a jump,drove 1 mile and went home. The next morning the barrey was totally drained,igot it charged overnight, and it ran fine for a few days, now the light come on, but it won't start, i don't here anything when i turn the key, what miight this be?

Asked by for the 2002 Mercedes-Benz C240
possible battery or alt have it tested. how old is the battery? could just be going out as internal plates short