If your flight controller has NO lights whatsoever when you plug in to your computer, then its most likely dead, dead.
You may still try the solution below if you like, good luck =)
If your flight controller has a solid blue light when plugged into power, it most likely means it has corrupt firmware or did not flash correctly.
To fix this, follow these steps.
- Short the bootloader pins, or hold the bootloader button. If you have neither of these, you can try without step 1.
- In Betaflight/Cleanflight click the firmware flasher tab
- Select the correct firmware for your flight controller and the latest version.
- Click Load Firmware [online]
- Select the following options
- Click Flash
Hopefully it should flash, verify and you can now connect and setup your flight controller again.