Not enough information.
Is this the first week out of the garage after winter storage ? In 95% of the cases the engine was stored with ethanol fuel in the carb, fuel lines, and/or fuel tank. Not only does old fuel not burn, but as it sits in the float bowl it will clog the jets that allow the engine to crank.... even if you dump the old and install new fuel. The engine is able to crank, but only because the carb FINALLY manages to deliver fuel after all that trying. You'll burn up your starter if you continue that route.
Get the entire fuel system cleaned at you local mower shop. You and 300 of your closest friends and neighbors are already there with the same issue.
