1. Please check if you have turned on the 'loop recording' in 'record setup'. 2. Please check if there are many event videos locked in the 'Event' folder? If so, please delete those files and adjust the G-sensor level. Please note that those files in 'Event' folder can not be overwritten, but need you delete them manually.
3. Check if your SD card is the one we recommend. Please note that some cards like sandisk and transend may not stable enough for HD video.