Lawn mower starts, but that's all it does.

[Mike Johnson]

First, check the air filter -- just pull it off and see if it runs without it. A clogged air filter could cause it to start and die just like you describe.

It could also bad fuel, maybe contaminated with water. I'd drain it and fill it with fresh.

Then if it still won't start, I'd suspect the carburetor. It could need an adjustment, or a cleaning, or a rebuild.