First, close the lid of the unit without placing a bag in it. Start the appliance and let it go through its cycle. When the unit stops, gently touch the seal bar. Is it hot/warm? If the seal bar is not hot or it is too hot (and the bags have melted), then there may be something wrong with the sealing bar. Are you trying to vacuum package items that are not moist? If so, test the bag by placing a spoon in a bag and place the end of the bag into the vacuum channel, close the lid and press the ON button. Lock the side clips or press down on the lid and allow the unit to go through the entire cycle. If the bag seals, then now you are able to vacuum/seal bags. (If the bag seals, you are now able to vacuum/seal bags.) Are you trying to seal moist items, such as unfrozen meats or fish? Try placing the meat or fish in a bag, then taking a paper towel and folding it in half twice. Place the folded paper towel into the bag so it is between the item and where the bag will be sealed. Place the open end of the bag into the vacuum channel, close the lid and start the vacuum/seal process. The paper towel traps excess liquids and won't affect the flavor of the food item. If the unit seals properly, then you should be able to vacuum/seal bags. You can also slightly pre-freeze meat or fish for 15-30 minutes in order to eliminate some of the juices. While examining your appliance, check the lower gasket for any cracks, dents or food particles. Please clean the gasket by wiping it with a cloth.