why wont it start

I have a 2010 c-300 that just failed on me last night. Power was available at the battery, but when you turn the key it was dead, no sign of life. Steering was locked and it was stuck in park. Also noticed the key stopped locking doors, etc. Was an hour+ from home and wound up getting it towed that cost me $300. When I went out this morning, I tried my second key and it worked fine. I suppose this is a key problem vs a car problem... gives you a reason to tote around your second key.