Anti Lock Break Light ?

O.K. I'm not sure if you meant 2007 fortwo.......or 2008? Either way, what you're describing sounds like the Tire Pressure Sensor Warning Light. This light comes on when a tire is losing/has lost pressure. The button that you're referring to under the radio is the RESET button for the Tire Pressure Sensors. So.........if this light comes on when you start the car, it's either indicating that you've lost pressure in one of your tires, or the system is malfunctioning. If it illuminates continuously, then one or more of your tires is under-inflated........if it flashes, there's a malfunction in the system. When you press the reset button, you're telling the system that whatever the amount of air (currently) in your tires is basically, the correct amount, so the light will go off. If you come back out later, and the light is on again, it's a good indication that you may have a nail in your tire or something that's causing it to lose pressure. So..........first, check all of your tires with a reliable pressure gauge. The front tires should be approx. 29 lbs. of pressure, and the rear should be 36 lbs. of pressure. If any of your tires are significantly lower than that, you've probably got a nail/screw/leak in that tire, which would need to be repaired. Air up your tires to proper inflation.......press the TPMS RESET button, and everything should be alright. Hope that helps!