2005 BMW 325 Won't crank

2 days ago, i turned my car off, hit my power button on my radio to listen to it with the car off. 20 minutes later, car wouldn't crank. Husband jump started & it's cranked and drove fine for 2 days. This morning, car just clicked when i turned the key. I was told by a friend that also has a bmw that it was because i hit the power button on my radio & that's what has shut my car down because she had the same thing happen to her a couple years ago. Have you ever heard of this? I'm having a new battery put in tonight but if the problem is with the anti-theft system in the radio button, I'd like to save my money on the new battery.