When a board looks dead, do not start by rewriting firmware and do not start by swapping random parts. Start by proving the board is alive enough to deserve software attention.

• Measure every primary rail and note sequencing
• Check reset, enable, and power-good signals
• Confirm oscillators and clock outputs
• Look for shorted rails, hot components, and current spikes
• Verify the debug interface electrical basics before blaming tools

Post the first five measurements you took, not just the conclusion you reached. The quality of the fault-isolation discussion depends on that.