Arduino startet nicht an externer Spannungsquelle

[HaWe]

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Ich bin trotzdem der Meinung das es mit der Stromversorgung zusammenhängt.
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Vin wäre der 5V Eingang/Ausgang.

das stimmt so nicht, Vin ist das was man per Cinch Stecker anschließt, also an den Spannungswandler:

VIN: This should be above 6.2V (since the dropout voltage is 1.2V) and preferably between 9V and 12V.

VIN is the completely unaltered input power before the regulator (it will be useless if regulated 5v is supplied directly).

Vin is the voltage powering the arduino. If you hook it up to a 12V power supply the Vin pin will be 12V.
5V is the 5V power coming from the onboard regulator. If you hook up the arduino to a 12V power supply this pin will still be 5V.
If you're using a regulated 5V power supply they're interchangeable, though from my understanding you can use the 5V pin if you want a bit of overvoltage protection or the Vin pin if you need a bit more power (where you're limited by the current limit of the traces, not by the regulator).
It's important to note that both pins are not outputs - you can put power through them as well.

"RAW" hingegen ist eine Bezeichnung, die Arduino.cc nirgends anführt.