[Solved] Why does my circuit turn off the onboard LED (Nano)?

I’m building a project around an arduino nano and every time I attached a new arduino to the board I found the onboard D13 LED would fail. I thought they were defective, changed a few, eliminated a connection to reset pin but finally isolated the problem to D13 itself.

I have a duinotech arduino nano v3 that is powered by USB or a 9V battery to Vin. I am using the example “Blink” code. D13 is going to drive an LED circuit so I have connected it to the base of a 549 NPN transistor. The emitter is currently connected to ground and the collector is currently floating. When I disconnect D13 from the transistor the LED works again. I added a serial print section to the code to double check the program was running and it is.

I mainly want to know why this is happening. The onboard LED is not essential but I want to make sure the circuit will work and it’s not going to cause any other problems with the arduino.

Henipah:
D13 is going to drive an LED circuit so I have connected it to the base of a 549 NPN transistor.

Hopefully with a resistor in between.
Without a base current limiting resistor D13 is shorted to ground via the BE junction of the transistor, and the onboard LED won't light up.
Post a diagram showing how you have connected things, so we don't have to guess.
Leo..

That was exactly how it was connected, I’ll try with a resister.

Yep, 1k resistor fixed it. Totally forgot one, thanks.