Headlights and radio work. Battery juice is getting to them.
Are headlights nice and bright, are ALL of the electrical circuits in the car OK??

If you have another car try with the battery of your second car, that would rule out the battery if it does the same thing.

Some times the fuses look good, still I would replace them. They are cheap.

Remove cover for black box behind fusebox, touch each relay to identify which one is "buzzing/humming" and remove. See if it cranks. Put it back and retry to cranck.

Read the numbers on the relay and post them, may be someone knows its function.

Pictures are worth a lot, location of relay etc...

These are steps that I would try, by no means I am a car technician, but I would try to eliminate posibilities one by one.

Starting with the fuses, then the battery and so on..

Keep us posted.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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