There's an icon on the app to switch between stills and video, however if you just press the record button on controller it should go to video on its own.
Definitely try format SD card but I'd have thought it would tell you if it was too full. 
There will have been several updates to app and firmware since you used it before, but I wouldn't be messing with that without some research - though generally being all on latest is best option. Mismatches can cause complicated issues though.