What system are you on? Are the save files still in the www/save folder? In that case you might be missing the global file, which tells the game which save file is in which save slot. To fix this, move all saves out of the folder, open the game, create new save files in all used save slots. Afterwards you can close the game and overwrite the new saves with the old saves files that you moved out of the folder earlier. The previous in the loading screen will be wrong, until you load and save it again, but the progress will be there. Make sure the game is not on a write protected (="read-only") location on your system or an usb stick. In such a case, the game would be forbidden by the system to create save files.
