If the heater kicks on but the fan doesn't blow, it could be either the fan/blower unit or the controller circuit card in your heat pump unit. If the heat doesn't work but the fan blows, it could be the heater core element. In today's homes, there is a small breaker box near the outside heat pump. Turn the switch off, Remove the access panel from the outdoor unit and look for any obvious burns on the circut card (don't touch it). Look for a schematic diagram on the inside of the panel. Look for any resettable fuses, fuse links or regualr fuses. Examine the fuses to see if they are blown. If one is blown, replace the fuse. If the fuse blows again, something on the circuit card is bad, causing the fuse to blow and you will need a new circuit card. Note the model number and the serial number of your H-AC unit and call the manufacturer for advice. It could be under warranty. Either way, you will probably have to call a heater-ac guy to fix it for you. It is unlikely H-AC people will troubleshoot it for you over the phone since customers are their lifeline. I recently had a blower unit go bad in my upstairs unit. It cost less than $100 to have a guy come out and repair it.
