Hey Dounia,
Did you by chance drop your GoPro? It looks like some of our community members have experienced a similar problem. You can read this thread for reference: [post|271836].
Here are a few things you can try:
* Check if the battery terminal where the + side of the battery is loose and if the spring tension is not holding the battery in place when inserted
* Replace the battery doors if they are loose
* Remove the SD card
* Try a new SD card
* Upgrade the firmware
* Open the device and look for any loose connections