Okay so I bought another Neopixel with 60 leds and I knew my trafo can't handle that amount of current. So I also used another stable 5V power supply, which worked with my arduino and neopixel. I also tested the previous (broken) neopixel, and I saw that these also worked. I think the problem was that my previous power supply couldn't handle that much current. So no issues with wrong wiring (I didn't use 470 ohm resistor as well as capaciter).
Thanks all for the comments and your time!!