Please Help!! 2000 C280 novice

2000 Mercedes Benz C280 - Noticed I had a BAD coolant leak when I pulled out for work a few days ago... I added more coolant, and After a few minutes of driving, begin to hear a noise from under the hood. I popped the hood and the Automatic Belt Tensioner was no longer spinning and was beginning to smoke. I also noticed coolant leaking rapidly once again. what's wrong with my car??!!?!