Backup EXEC during a restart, files corrupted

My 2008 server running ver 12 of BE, was doing its normal backup. It appears at the same time windows was doing an update, then it restarted the server. Now the files that were in the folder for backup, that had not been backed up, are no no longer useable, these are all files, Office type, AutoCAD and many more. How do I recover or repair these files. The backup copies over the tape from the backup the day before.

Thanks