First of all, please replug the power supply and try again. It is better to power it with 9V input.
Then please check and re-plug the ribbon cable connection both on the electrical board and on the sensor board to make sure they are stable and with no damage on the connectors.
Also, please format your SD card and also try other qualified SD cards. It is better to try with SAMSUNG U3 cards and format them to exFAT or FAT32.
At last, please update the firmware via SD card by referring to: https://www.runcam.com/download/runcamhybrid and restart the camera.
If nothing helps, please show us a video for the abnormal situation you met, clear pictures of both sides of the PCB and also your purchase record including the order date via email: email@example.com.
I have same problem and have tried and checked everything it says to. If I use it first time that day it works but after that nothing then next day it will work the first time then nothing again.