HEEELP! 32GB Extreme SDHC not being read by anything...?

Yesterday I was recording some footage for a little project I’m doing. It was all fine n dandy, but this morning when I went on my camera to re-watch the videos I had on the SD Card, I could only view them once, and then it said ‘could not playback’?

So I put the SD Card into my Mac to watch the videos on there, and all of  a sudden it comes up with a message saying

’The disk you inserted was not readable by this computer’.

It can’t even be recognised on my camera anymore.

Please help, I was really happy with the footage I’d captured and would be gutted if I lost it.

(Also I’m 16 and not very technologically capable so if all advice could be explained as simply as possible I would be very grateful)

Thank you xo