If your system shut down or crashed mid-save then the file will be corrupted and cannot be fixed.
Likewise if you game has been force closed for any reason there is a chance of save game corruption.
The only opportunity to get the save back is to try and use Windows ‘Restore Previous Versions’ function. This will not always be on by default so may only work for some users.
To use this functionality, first go into your 'Documents' folder. Within there should be a Sports Interactive Folder.
Go into the Football Manager 2016 folder. Go into 'games' and right click on your save which no longer loads. In the menu that opens is an option called 'Restore Previous Versions', click that and see if it works. It'll first scan for a previous version then potentially give you the option to 'Restore'.
To make sure you don't have an issue like this again, we'd very much recommend going into your in-game preferences when you load up FM and turn on 'New File for Every Auto Save' option under the auto saves. We'd also suggest turning it on onto weekly or fortnightly so you always have a recent back up in case of any problems.