Not sure I can help - depends on the file a bit. But you can try doing a Save As.... and renaming the file and saving it to antoher folder (it could be open or have some other issue). You can also trying Duplicating the image Image>Duplicate and then try saving it. If nothing is saving at all... you probably have to restart Photoshop. But its possible Photoshop has saved your file for you since it has an auto-save feature that is every 10 minutes by default.
Try seeing this post about recovering your file if the above steps fail.