Trouble programming without bootloader

Hi guys,

I'm still very new at this so please bear with me.

I'm trying to program my Arduino Pro Micro without a bootloader, using my Arduino Uno with 'Arduino as ISP' as a programmer.

The actual programming of the board goes smoothly and when connected to the 5V output of the Arduino Uno, the Pro Micro works as it should, creating a serial port over a USB cable connected to my computer. However, when disconnect the 5V jumper andI only connect the USB cable, the only thing that happens is that the power LED lights up. No code seems to be run.

What am I doing wrong?

It turned out I hadn't made all the necessary disconnections from the Uno. Even though the Uno wasn't powered I had to disconnect the jumper connected to the reset pin of the Pro Micro. I don't really understand why that is but at least now it works.

You are powering the Uno from the ProMicro via the data lines. The pins of the micro controller are protected with diodes to Vcc and Gnd. Keeping a data pin connected and that pin being high on the ProMicro can power the other (Uno) side via the diode.