My key will work and then will not work

If you are talking about the key not turning sometimes, there are 3 main possible causes. 1) The key is worn out. Try a second key. Perhaps have a new key cut from the original key code to see if it turns more freely. 2) The ignition cylinder has worn or stuck tumblers inside that prevent proper operation at times. The cylinder will need to be replaced. 3) The shift interlock is not working properly - the shift lever is not reaching the "park" position as it should. If the shift lever is not securely in "park" then the ignition cylinder will not turn. However, keep in mind that the ignition cylinder will also not allow the key to be removed either -- if the shift lever is not securely in the park position. Have this checked locally - check this link to find some shops near you: www.repairpal.com/repair-shops