Murray select lawn tractor will turn over when I try to start it, but will not start up.

Was it running and then just died, or has it been acting up, what is the symptoms involved.

Do you have spark through the spark plug, is the spark plug wet with fuel when you have tried to start it, then immediately removed the spark plug? Have you pulled the carbs float bowl and inspected? Has the unit been stored outdoors? Has it been stored or not run for quite some time? As you see I need more info.