The first thing to check on your Troy-Bilt self-propelled lawn mower is the stop switch wire or cable to make sure it is not broken or has come unattached. If it has broken, then it would need to be replaced, however if it just came unattached reattach it.
Next, test the stop switch using a multimeter to see if it is bad. If it is, it would need to be replaced.
You can find the model and serial numbers located on your Troy-Bilt push or self-propelled lawnmower on the deck, or on the rear door of rear discharge units.
NOTE: if you need a part for the small engine in your Troy-Bilt push or self-propelled lawnmower, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Troy-Bilt push or self-propelled mower. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: