Check if your toolhead cable is correctly seated (switch off machine before - people have damaged their controller and toolhead by accidentily inserting the toolhead cable wrong way around with machine turned on), and also check if the connector of the hotend/thermistor is still well connected. I suppose the latter has a certain chance to get dislodged by your undertaking. If all cables are sitting well and still it does not work:
attach another toolhead (to double check that your toolhead cable is issue free, and also the controller is working)
Closely inspect if any wire has broken from your thermistor (and potentially also the heater)
If you have, as a test replace your hotend with a spare one - does it work then?
This should help you getting closer to the root cause…