I have several machines that have sat for longer than they should have.
My guess would be stale fuel.
I was fortunate. After draining the fuel tanks, as well as the float bowls and filled them with fresh fuel with stabilizer added, I was able to get them fired up.
I removed the air filter and added a small amount of fuel to the air intake, reinstalled the filter and cover and pulled it a few times. One machine in particular required this several times before it continued to run.
All are running perfectly now.
Kirsten, you should only buy fuel in small quantities for lawn equipment. Having it sit around in cans is a bad idea, especially the newer fuels with Ethanol added.