Dags
Maybe you should try copying any data from your computer to your card, just to make sure your card(s) will accept the data.
Then just erase the data leaving a blank card. To date I have never formatted my cards. If you can record on the card(s) they should be good.
If you are still not sure, purchase another Sandisk card at Walmart and use it without doing anything to it, it should work.
Put the card back in your machine an try to record on it by getting to the "Snap Shot and Recording" screen, hit the Menu button and start recording the unit will tell you if it is recording, then you must hit the menu button again and stop recording before shutting the unit down, otherwise "End of File" will not be recorded and the recording is rendered invalid.
George