my radio even stopped working
all my warning sounds including turn signals stop working. no sound is heard on 2008 Chevrolet Cobalt
Do your head lights turn on or starter even attempt to turn over the engine? Try jump starting the car from another car see then if your engine then cranks over. Check that your battery connections are clean tight and secure. It could be many things a bad battery, broken fan belt, bad alternator or wiring/fuse issue. Turn on the ignition switch to the on but not run position do you see an icon on the instrument panel representing a battery, if you do not see this battery icon the alternator is not seeing power to allow it to charge. Start the engine does the battery icon go out. Put a volt meter across the battery terminals with the engine off, at rest the battery voltage should be 12.6 volts if the battery is fully charged. Now get a friend to start the car while you watch the voltmeter, the voltage reading across the battery should read approximately 14.6 volts if the alternator is charging correctly. If the alternator is charging properly and the battery tests OK then you may have a "parasitic draw" on the battery. A "parasitic draw" on the battery is something that stays "live" stays switched on even through the car is turned off and the keys are out of the car.