I was installing a programmable thermostat & not the unit doesn't come on anymore. I did blow a fuse y the furnace so I replaced it still nothing. I tried putting the old thermostat back on but that didn't work. Is there a reset button some where it is a carrier unit not even 2 yrs old.

No reset button that I am aware of. Recheck the fuse and recheck your thermostat wiring. Since you changed the thermostat it is more than likely to be the cause of your unit not running since you replaced the fuse.

Is there a float switch in the overflow drain pan under your air handler that you may have accidentally hit or moved? Some installers connect these to the R wire and it will shut down everything.