Why LED3 from my STM32F407G Discovery is blinking when I switch arguments SERIAL_RX and SERIAL_TX?

Why LED3 from my STM32F407G Discovery board is blinking when I switch arguments SERIAL_RX and SERIAL_TX from my code Serial gps(SERIAL_TX,SERIAL_RX)?
Also, I have the same problems with my 10 DOF LSM303DLHC from Adafruit when I connect the PB9 and PB8 pin from the STM32F407G Discovery respectively to SDA and SCL chip’s pins. I don’t how to know if my board is communicating with my chips.

I’m using a SparkFun Venus GPS with SMA Connector connected to a STM32F407G Discovery board.

The original code is from the project librairy: gps_settings_venus made by eisei taro . The main.cpp is also from eisei taro’s library (GPS_setting_Venus_Helloworld). Both can be found easily on ARM MBED site. Here’s the link to my ARM Embedded code on my GITHUB repository: https://github.com/EtienneMathieu/LEDBlink.cpp.git

Also, my entire ARM Embedded project (including LSM303DLHC and other chips ARM embedded codes) is located at that link: https://ulavaldti-my.sharepoint.com/:u:/g/personal/etmat3_ulaval_ca/EZXa0yuimA5PgKggnM96MsYB-YEQeUGqO8YXdRj_BwuBJQ?e=GfNdjo

Any help to improve this code will be well appreciated.