Exchange 5.5/Outlook Shared Calendar Sto

Recently we had our SB Back Office 4.5 Main HDD Boot Sector fail. It would loop continuously to the NT4 OS Start and would not boot. We took the drive offline and booted using the mirrored drive, which worked. However we immediately started experiencing problems with users who had shared Calendars not being able to use their Calendars at all. We have some ideas, but would appreciate it if anyone else may have some ideas on what this could be, corrupted data, missing data, and/or what they may have done to fix the problem.