New
#31
While I have no idea about what caused the situation, I do have an idea going forward, not one of prevention, rather, one of recovery:
If you have not already been doing so, please make routine (bi-monthly or weekly +-) full image backups of your OS and Data partitions onto any affordable, reliable, external media. There a number of free and pay-for backup / restore utilities you can experiment with and settle on just one or two of them.