Arduino uno turning off when 5v pin is entered

Your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advice on) your project :wink: See About the Installation & Troubleshooting category.

How many LEDs? For WS2812B, count on 20 mA per colour per LED. Full white will in that case be around 60 mA per LED.