quantum power 5 hp lawn mower?

I checked the oil-fine, checked the gas-put some in, pushed the button 3xs, held the handle, pulled the cord and it started---then shut off. I repeated the above starting with the button pushing--it started then, shut off again. I don't understand why it would start then just shut off like that. I have never had a problem with it in the past. It always just fired up. Now that the grass is getting long and I want it cut, I can't cut it. It's not too long as to make it difficult for the machine to cut, I just haven't been able to cut it for a week and a half. Please help, I want my kids to be able to play out in the back yard today. It is such a beautiful day!
thank you