Engine stalling and other problems

For a few days my car has been doing some weird stuff. The first thing I noticed was my cd player was screwed up and it made the music sound horrible, I unplugged it, plugged it back up and everything was fine. Later on I realized everytime I was about to stop like at a redlight, my car would die when I started going slow and the brake light and check engine light would flash on. This isn't a very big deal all the time, except for when you're already going around the curve and lose powersteering. Another thing i've noticed that's changed has been the beeping sound that stays on when the door is open with the key in it or the light is left on, that's completely gone. I don't know what happened to do it all the sudden but it's frustrating and I need help fixing it, thank you.