Deleting files from camcorder is just like clearing the recycle bin or Trash onyour comptuter. The data itself isn't deleted, just the area containing the deleted data is also now marked as free space so it is available for any new data to be written there instead. So a simple delete won't make your videos erased permanently.
As a result, you have chance to retrieve those deleted videos as long as the video data on your camcorder(memory card or hard disk) are not written over. And the best way is to try some video recovery software, recommended Asoftech Data Recovery as it helped me before, the program can also recover photos and music.video photo recovery program
First of all you need to install the program on your computer, then connect your camcorder (memory card or HDD) to the computer and start to recover your deleted videos.