My PBP starts up like a 1977 Chevy Nova

[KC9UDX]

Putting electronics that seem to fail or work with time in the freezer is a good diagnostic. Things that change with time are usually due to heat. Changing the starting heat (either warm or cold) can help isolate temperature change as the actual problem.

Is your non-working SD card slot plugged in? If so, unplug it and see if anything changes. Your non-working SD slot may be contributing to your problem.