Why is my ac/heater not working at all.

Why is my ac/heater not working at all. i have a 1999 chevy cavalier recently the AC and heat both quit working all at one time. none of the settings work at all. i already replaced the heater blower relay in the fuse box. my wife said it made a loud noise before it quit blowing air while she was driving. what are my options on this? what could it be?