Nothing blowing from my heat or AC in my 1999 mercury sable what could be wrong ?

If you mean that the fan isn't working at all - it's usually a failed fan. Sometimes the switch on the dash goes bad but I'd start with the blower motor.

Ok so I replaced the blower motor n it blows now but now no heat? What now could be wrong?

A clogged Heater core, low coolant in the engine, A blend air door actuator that is broken, AC Compressor that runs constantly. Check the simple stuff first: Is the engine getting warmed up after 5 to 8 minutes of driving? (Top hose hot to the touch and pressurized) Check the temperature of both of the heater hoses: are they both hot or is one cooler? If one is cold and one is hot, flush out the heater core with a garden hose and recheck. Is the Thermostat missing or stuck open or the cooling fan running constantly?

I changed my resistor and my blower motor was xhanged the car get hot i can feel the heat for car but its not blower and when on cold air it get cold but won't blower