Sometimes runs properly sometimes don't

Every time I upload my program on arduino it is always running ok, but when I power through a different source than the USB, I have to press the reset button and check if it is doing what I want. Any guesses so I can have my arduino UNO doing what every time I power on?

It should just work when connected to any source.

So which Arduino?
What does happen when you connect it?
What power supply?

Also attach your sketch in case there is any minor issue with that please but use the CODE TAGS ( </> to do so.

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I'm making the AD conversion of a inverter a powering my arduino uno on it. As I make my conversion, I display on multiplex 2 cathode display, the info I got.

We await you answers to questions already asked.