When I set the thermostat to auto, nothing happens but the fan will run if I keep it ON

Need more info. AC? Heat? What is the room temp? What is the tstat set temp? Is it a heat pump or what type of system? New install or new problem on old system? Anything else you can add?

New problem, old system. Just started yesterday. Room temp is as high as 80 and I set the temp as low as 50. A friend just came over and "messed" with the inside of the thermostat box (little blue and red wheel) and now NO cold air comes out at all. Went down and reset the circuit breaker for the ac unit AND the furnace and now NOTHING will come on. I'm totally messing it up?

Ouch. Sounds like your friend didn't do you any favors. I really can't help you as I don't know what type of thermostat you have. Is it a mercury bulb type (analog) or electronic (digital display)? You could be having electrical problems in the electrical control section of the air handler. Or the problem could be bigger than that (hopefully not :) ) Most likely it won't be terribly hard to troubleshoot for a professional, but it sounds like that type of problem unless you are comfortable using a DVM and reading electrical schematics. I can help you with specific troubleshooting questions but I really don't have the time or energy to type out my complete diagnostic routine. :D