Overfull bag caused shutdown-will not restart (by 2 users)

There can be quite a number of causes for these problems. A lot of the time there is a clog that the consumer has not found. If the motor sounds like it is running at a high pitched noise, and there is low or no suction, then that's your problem.
With the over full bag problem, I might have to know a little more information. There may be a reset button on the machine. You are going to want to check around the base of the machine where the brush roll is. Also, a good thing to do is to just change the bag and give the machine about 15 minutes before you turn it back on. It's high unlikely that you shorted-out the thermal protector with one time of not changing the bag.