Some repair / testing tips to verify this is the part you need:
First thing your going to do is test for 240 vac at the wall outlet to verify that your getting the correct amount of power to the dryer. If your only getting 110 vac then the dryer will still run but won't heat, it can also cause your dryer to not run or heat. If your not getting 240 vac at the outlet then you need to check your breaker or fuse box.
If you are getting 240 vac to the dryer then you will want to unplug the dryer, undo the vent from the dryer, and remove the bottom panel from the dryer. If you want to make a little more room you can remove the blower cover that the lint trap slides into. Now make sure the dryer is unplugged and you have a digital multimeter, or a analog ohms meter. Remove the two power leads on the terminals of the heater element, set your multimeter to a continuity test, or your ohms meter to test for ohms, and test at the 2 terminals of the heater element. If you get no continuity, or 0 ohms, then you need to replace the heating element. You will find the heater coil burnt in two somewhere when you remove the coil from the dryer. Make sure you clear the blower housing of any lint build up while your in there and clear the vent from the back of the dryer all the way out of the house to protect the new heater coil. A good indication that this caused your problem is long dryer times before the dryer wouldn't heat at all.
If you do get continuity or ohms, you will need to test the the thermostat and thermistor mounted to the same casing the element is inserted into. Just remove the wires from both parts and run your continuity or ohms test. If you don't get continuity through one or the other then replace it.
If these test okay you can turn to the heater relay on the control board and run a continuity test through the relay. The heater relay is a larger black piece with a large guage red and large guage black wire connected to it. If you get no continuity through the relay then replace the board.