Its only blowing out cold air what could be wrong

First thing I would recommend is to reset the furnace... by turning the power off to it.. waiting a minute or two then turn it back on.

Sometimes that will clear a fault. If it doesn't you might need to call a professional tocheck it out.

Lots of options here. Is there a diagnostic light blinking on the control board (may be a site window that will allow you to see the led light through the cover of the furnace). We need more info to be of any assistance. Try doing as smoothy suggested, and if that fails let us know exactly what the unit does when power is turned back on.