The MPU6050 module of dfrobot.com is commendable documented but the OLED lacks any relevant documentation. I guess the software isn't really the problem. Try uploading the software you use for the MPU6050 (alone) and attaching the OLED afterwards. I expect the MPU to stop working as soon as the OLED is attached. If the OLED board is built as I assume the use the 5V as Vcc and have pull-ups to 5V. So the I2C lines have a passive voltage of around 4.5V which may already damage the MPU6050.
It might work better if you connect the VCC pin of the OLED to 3V3 instead of 5V.