I don't own an laundomat or appliance business but I always seem to get the call when it comes to appliances... First, check your vent pipe and make sure its not clogged. If so, check the outside flappper to make sure its swinging free. If the flapper is not moving then you might have a clog. A moderately powered electric leaf blower jammed into the vent pipe on the inside of the house might be enough to blow the clog out. Usually a bird's nest but maybe also just build up from not being cleaned. There are also snakes you can probably rent from, like, Home Depot but so far the leaf blower has worked for me. Please dont' use a gas leaf blower in your house. ;) Beyond that... What make/model and is it gas or electric dryer? Each make/model has its quirks. The set of root causes is often general but the way to address the root cause varies. The electric dryers often have a thermistor which gets tripped if the vent has clogged and the dryer overheated. For gas, the thermistor often has a reset switch. In my experience the electrc ones either require a new themistor ($7US) or you can take them out and slam them flat on the ground to reset the little bit of metal inside which acts as the safety mechanism. Sometimes that works for ages and sometimes it just buys you the time to get a new thermistor.