haha i did that once too, except i was using Movie Maker (no, i cant afford Vegas, sorry) and saved the PROJECT, not the mp4, and proceeded to delete the footage. Had to redo the whole video, it was great.
But I would suggest going into the Start Menu and putting in "Restore." A result should pop up with "Create a restore point." Click on it, and an option should be available to do a System Restore. If the option is grayed out, you don't have any system restore points, and you're out of luck.