If your camera has Dropbox or other cloud backup, you can try looking for the files there.
If not, you can try chkdsk /f /x s: from the command prompt (replace s: with the drive letter of your SD card reader) to try and repair the SD card. This might work if the problem is only in the file structure and the data itself has not been corrupted.
Finally, if you are using an SD card bought at a bargain basement price, it is possible that the card's actual capacity is much less than that advertised, in which case the video files will not be recoverable.