One of the most common issues that users will endure with a lawn mower is when the engine refuses to start. There are a plethora of reasons to why this may be happening and if it does happen to you, reference this to see if the following issues are happening. For starters, if you have a gas model and it does not have an automatic choke system or no-prime engine, ensure that you have primed the engine and that the choke is on. For electric models, on the contrary, ensure the battery is charged. Now that the more obvious issues are out of the way, it could be an issue with the spark plug. They do not last forever and it may need to be swapped out with a new plug.
Along the same line, ensure the air filter is cleaned as this can make the machine much easier to start. Lastly, make sure you have fresh fuel inside that is no longer than 30 days old.