Here are some troubleshooting steps that you can take for this dryer problem:
Check the lint screen for the dryer. Make sure that it is changed before every drying cycle. Dryer softener sheets can cause a waxy build-up on the lint screen that can restrict air flow through the dryer. Wash the lint screen in warm soapy water to remove this type of build-up. Try the dryer again after washing the lint screen.
Venting problems can also cause long dry times and heating problems. Check the flexible vent behind the dryer for kinks or clogs. Check the exhaust duct to the outside of the house for clogs or restrictions. Make sure that the outside exhaust hood is unobstructed and working properly. If you suspect that venting is causing the long dry times, you can test the dryer by disconnecting the exhaust vent behind the dryer and allowing the unit to vent directly into the room temporarily. Try drying a medium load of towels with the vent duct disconnected. If the towels dry normally, then the exhaust duct system is causing your problems and will need to be cleared for the dryer to operate properly. Reconnect the dryer vent to properly exhaust to the outside of the home following this test.
If you are still having problems after checking the issues above, then you could have a component failure in the dryer. A bad heating element or a problem with the thermostat could cause this problem. I recommend calling a service technician to diagnose and repair the dryer if it is apparent that you have this type of component failure.