The dryer will not stay running.

When you hold the start switch you are energizing the start winding of the motor. If the motor does not take off and run, the most likely cause is the centrifugal switch inside the dryer's motor is not being switched. It is switched by a spring loaded collar on the motor shaft which moves when the motor starts to run, and again back when it stops. Often times this collar begins to stick on older dryers. Sometimes you can free it up by cleaning the dryer motor with an air compressor and hitting the collar with some spray lube. This only works some times. The only sure fix is to replace the motor, which unfortunately is rather expensive and a fair amount of work. Please don't bother rating this, as anything but a Fix-Ya lowers my score.