You are using an SD card reader/writer. That is an SPI device. That means that it uses pins 11, 12, and 13. That means you can NOT use the onboard LED for ANYTHING. Or pin 13.
You are using an SD card reader/writer. That is an SPI device. That means that it uses pins 11, 12, and 13. That means you can NOT use the onboard LED for ANYTHING. Or pin 13.