Sketch will not run after removing USB cord

I am new to Arduino and am having a problem running a set of 30 RGBW LED's without being connected to the computer. I am using a 12V DC power source and the sketch is working when the USB is connected but stops working when I remove the USB. I have verified that the power cord is operational and have also attempted to use a 9V battery. Any ideas on what the problem is?

Any ideas on what the problem is?

How could we possibly know anything about it? What of it have we ever seen? Don't you think showing it to us would make more sense than asking us to diagnose it without knowing anything about it?

Post your code and your wiring. You've obviously made a mistake somewhere. How you think anyone would be able to tell you what that mistake was without seeing what you've got and only from your vague description is beyond me.

My crystal ball sees a blocking while(!Serial.available()) in setup().

I hope you're not powering the LEDs through the Arduino.
Post a diagram.
Leo..

Not even my Tarot cards are telling anything….