While changing the light bulb on the bottom of Whirlpool MH1140XM, the bulb popped. I replaced it but now all I get is a hum whether I push timer, light or oven settings. The oven appears to be heating but the turntable doesn't turn.

You are lucky!

MICROWAVE OVEN LIGHT Remove the louver per instructions 1-3 above and charcoal filter, if used.
1. To replace light bulb, first disconnect power to the microwave oven at the circuit breaker panel or by unplugging.

2. Open light cover located behind filter mounting by carefully pulling up on the front edge.

3. Remove old light bulb and replace only with equivalent watt bulb available from parts distributor. Bulbs are also available at most hardware stores or lighting centers. DO NOT USE BULB LARGER THAN 20 WATTS.

4. Replace the microwave oven light cover by carefully pushing into place. Replace the charcoal filter, if used. Push the louver back into place (engaging both the bottom and top tabs) and replace the louver mounting screw.

When in doubt, refer to the manual :>D

https://d1vofmza27mmhi.cloudfront.net/product-pdf/frigidaire-fgmv174kf-use-and-care-manual.pdf

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If the model isn't manufactured any more you may have no choice.

Toss it out. The transformer is likely bad.

Since the microwave is humming, that tells me that the diode is bad and needs to be replaced.

Test the high voltage capacitor, the rectifier diode.or the magnetron.

The diode and capacitors can br tested. The capacitor must be allowed discharge before testing, or you risk to get electrocuted, even if power is off. Capacitors can get discharged by shorting their two contacts.
Replace the magnetron if the checks and all of the high voltage component tests are good, but the unit still does not heat.

All locations, and description of this parts can be located using the diagram here: Counter top.

Parts must be tested to find out what is wrong.

Remember that microwaves are potentially dangerous devices if not repaired properly, the job must be done by a competent person.
A microwave energy leakage test must always be performed when the oven is serviced for any reason.

Regarding parts, contact the seller here to purchase parts.

I left the unit unplugged over night, plugged it back in the next day and still had the same problem.

there is a switch on the front usually inside the back bottom latch it pushes on a switch in the back of it as you close the door.
you have to remove the top cover to get to it.
you can insert a plastic knife to test it. you should hear a click and light should turn off.
it may be jammed or open inside the switch .or wire is off. etc..

the door switch is likely stuck open.

We see (and repair) this a lot. The problem is on the control panel, which we regularly repair nationwide by mail for $39.95 postpaid.

This light failure often occurs when a bulb goes out and the filament shorts, or when the bulbs are removed or installed without first unplugging the oven from the power line. Either can cause such a failure on the controller.

This can often also affect the exhaust fan operation, too. The lights and fan can be inoperable or stuck on too.

Details of our service and critical safety information and disassembly information is at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk

We're happy to help and we appreciate your thoughtful rating of our answer.

William E. Miller, AS-EET
[email protected]
http://www.microwavedisplay.com

This is a problem with the control panel assembly, which we repair nationwide for $32.50 postpaid. Sometimes the bulbs short when they fail, and that damages the control board. This also can happen when bulbs are removed or installed without first unlugging the oven or turning off the breaker. For critical safety & disassembly info and other details of our service, see http://tinyurl.com/yzjozk