Furnace light once then won't relight unless I turn off the thermostat then it will relight once and the transformer stay on with a buzzing sound

Quiet buzzing of the tranformer is normal. Do you have any blinking lites on the control board? Try cleaning the flame senser with fine sand paper, sand cloth or steel wool.

Check the voltage on the output side of the transformer,who many volts, should be 24 at least