Make a backup! Before doing anything else. Preferably on another computer or CDR as a there is a slight possibility the hard drive in question is failing.

 A successful repair isn’t sufficient to ensure your data is clean.  I’ve personally seen a 120 Mb backend MDB repair just fine but both compacting and importing caused Access to puke on the same table.  We had to restore from last nights backup.  So you must compact it after repairing to ensure it’s clean. Importing all the objects, the relationships and the relationships window layout into a new MDB would be even better.  Also see After successful repair import into new MDB

Stupid Question – “Unrecognized database format”

Do you have multiple versions of Access installed on your system?  If so you might be opening a newer format of Access MDB in an older version of Access.  For example you are attempting to open an Access 2000 format MDB using Windows Explorer.  But if you last used Access 97 it will attempt to open the MDB.

If this is the situation then open Access 2000 first and use it to open the MDB.  Alternatively you can use Aylott Computing’s excellent AccVer.  Which I use all the time and highly recommend.   Or you can tell Access to stop reregistering the file extension by visiting Subject: INFO: Avoiding the default system.mdw loss when re-registering Access 97.

More info

Some corruption symptoms
Determining the workstation which caused the corruption 
Corruption causes
To retrieve your data

Corrupt objects, such as forms or reports One symptom can be Access crashes when you open a form or report in either form/report view or design view.

Links

• Access Web on corruption
• Allen Browne’s Preventing Corruption and Recovering from corruption
• Microsoft’s Knowledge Base articles, stuff and links on corruption
• Database password appears to be set Also see TSI Word to the Wise
• Access 2000: Corrupt VBA Project message during conversion
• ACC2000: Error Message: Error Accessing File. Network Connection May Have Been Lost – 304548
  One possible partial solution to this problem may be to use Access 2002 for all your work in an Access 2000 format MDB and only use Access 2000 when you need to do some testing and/or creating the MDE or use the Package and Deployment Wizard.
• Novell Netware and Microsoft Access MDB Corruption
• Multi-user Database File Corruption
• Access Emergency – Help Yourself
• Microsoft Database Repair Knowledge Base Articles

When all else fails – MDB repair companies

• PK Solutions Home Page Rebuilds corrupted databases usually within 24 hours. When you need him you really need him. A large number of folks in the newsgroups have stated that they were very happy with his services.
• Access Emergency (some useful general info) / Access Datenrettung
• Access Repair Center 24 Germany
• Data Revive
• Action Front Data Recovery Labs
• Access Data Recovery
• Msaccessrepair.com
• EverythingAccess.com

Utilities

• AccessRecovery is a data recovery program for Microsoft Access databases.  However it is likely more expensive than using a service.  Also at least one newsgroup poster has not had good results with it.
• AccessFIX from Cimaware
• DataNumen: Advanced Access Repair  (2006-11-26)