Blue screen of death after thermal runaway - fried motherboard?

[PLAyer_uno]

Hello all, While cleaning the hot end on my Ender 3, with the printer was on and the hot end at 215C, I must have accidentally caused a short circuit (guessing either the thermistor or the heater element). The printer started a continuous alarm tone and the screen displayed "runaway thermal... please reset". I immediately shut the printer off. Now every time I switch it on the screen does light up, but it's blank. Pushing or rotating the button has no effect. I've taken the cover off the motherboard and can see a blue LED light up when the printer is on. To test if the thermistor is the issue, I've unplugged it from the motherboard and plugged in a new one - no change. Read somewhere that an update to firmware could fix this, but I tried and it didn't.Have I fried my motherboard? Or is there something else that can be done?