Can't listen to AM radio on my Philips HTS3544!

That's right. AM radio stations disappeared. I cannot tune in to a single one now. I don't understand how this can happen. I believe, the antenna for AM reception is inside the unit. Maybe, using an external antenna would help. FM reception still works just fine. I am quite puzzled. Naturally, once you can no longer to listen to AM radio, AM radio is precisely what you want to listen to all day long. It's just human nature! Frustrating.