The designer who put two servo connectors on that L293D motor shield must have had a brain fade. Servo power on a L293D shield comes from the 5volt pin, and that's bad.
Only use that shield for tiny brushed DC toy motors, nothing else.
Continuing to use the servo through that shield could also release the magic smoke from the laptop.
Connect servo signal/ground directly to the Arduino,
and connect a separate supply to servo power/ground.
That supply must be able to deliver the stall current of the servo.
Sounds like a Sunfounder 55g from the limited specs you posted.
They have a stall current of about 1.7Amp. Way beyond USB power.
Leo..