L and RX diodes blinking and resetting sketch when arduino is powered via USB

I have a problem with my arduino UNO. After loading a sketch L diode blinks 3 times and then RX diode starts blinking for a moment, and it keeps repeating and resetting my sketch. It only happens when I power arduino via USB cable, it works fine on external 12V power supply. Its original UNO, not a chinese one.

Connecting almost any Arduino to USB causes a reset to be sent which restarts the sketch.
If that is what you are describing then it sounds normal.

External supplies dont cause that reset (normally)

Resets can also be caused by hardware glitches on the computer an Arduino is connected to.
Especially true if you are close the the 500 mA limit with lots of goodies bolted onto your Arduino.

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It will help you get the best out of the forum.

It doesn't only reset when I plug the USB cable, it resets all the time when its powered via that USB. I used a simple blink sketch (from examples in IDE). Sorry for my english its not my native language. So if I modify blink sketch a bit and make the diode 5s on and 5s off, the sketch will work normally for a few seconds and then diode will turn off after about 2 seconds and L and RX diodes will blink.

I actually managed to fix my problem, It turned out that my headphones drivers software caused this issue.

Thanks for getting back with that.
I doubt any of us would have guessed that :o