Calibre library is corrupt, can anyone help me please?

When I try to open Calibre I get the message that the database is corrupt and will attempt to restore. The restore fails with the following messages:

calibre, version 1.25.0
ERROR: Failed: Restoring database failed, click Show details to see details

Traceback (most recent call last):
File "site-packages\calibre\db\restore.py", line 125, in run
File "site-packages\calibre\db\restore.py", line 272, in replace_db
WindowsError: [Error 5] Access is denied


I have no idea what this means or what to do about it. Please can anyone help?