I just replaced the filter in my furnace. Prior to do this, my central air was working fine. Now, the entire system will not kick on. I tried fan only, heat and cool. The thermostat clicks on to work, but there is no sound coming from downstairs or outside. I have flipped all the breakers and even reset the blower. Any suggestions?

Did you remove the blower door to replace the filter? If so be sure that the door is correctly in place, there is a safety switch in place that has to be pressed in, did by chance shut off the ssu (power switch ) on the side of the furnace?