Mower ran out of gas when blade was engaged?

That's not much info to work with.

But, assuming that you are talking about a riding mower which quits when you engage the blades, I would tell you to check out the seat safety switch. For some readon the mower doesn't think there is anyone on the seat. It will not run with the blades engaged with no one on the seat. Somewhere attached to the seat you will find a small switch with two wires going to it. It may have come unplugged or it could just be a bad switch.