I recently turned on the "fan" to my furnace to cool my house since the windows were open. It wasn't doing the trick so I decided to turn on the A/C. It ran for couple of minutes then shut off. Now neither the fan, A/C, nor heat will turn on. I checked all the breakers and none of them were tripped. I switched them from off to on just in case and still nothing. Any ideas?

Sounds like you lost low voltage power. The newer furnace will have a low voltage fuse on the control board to protect the controls and transformer. If it blew it can be replaced with a simple automotive fuse of same size. You may have a low voltage short on the out side A/C or the thermostat wire going to it.