Crank no start

What is your question?

I started my car the other morning and it was about 29° outside. When I started it there was a loud pop under the hood. The car kept running so I drove it about 40 miles. Later that afternoon I went to leave and it would crank but no start I went and bought a battery and it started so I went back home. It's been 3 weeks and it still won't start. Now it's a slow rough crank with no start

How long has your 2004 BMW 325Ci had this problem?

More than a week