If the blower works but the air is not hot, the problem lies with the water flow through the heater matrix. Check the coolant level, check the operation of the heater valve in the pipe to the heater and if you can find nothing wrong flush the heater matrix with a hose.
If the coolant level has been alowed to get low, you may need to bleed the air from the system as this will stop the heater from getting hot and will make the engine over heat.
Lack of heat could also be caused by the heater controls not working properly - perhaps some linkage has fallen off.
If the problem is that the fan itself does not work, see - http://forums.mg-rover.org/showthread.php?t=55979
First thing to do if you have a misfire is to fit new plugs and give the rest of the ignition components a good clean.
If the coolant level has been alowed to get low, you may need to bleed the air from the system as this will stop the heater from getting hot and will make the engine over heat.
Lack of heat could also be caused by the heater controls not working properly - perhaps some linkage has fallen off.
If the problem is that the fan itself does not work, see - http://forums.mg-rover.org/showthread.php?t=55979
First thing to do if you have a misfire is to fit new plugs and give the rest of the ignition components a good clean.