My notebook was infected by adware/virus, all the famous antiviruses
and anti-spywares failed to eraicate it. Before I made a decision
about formatting the hard drive to get rid of the virus, I had noticed
that my outlook express began to act oddly; one time the inbox showed
1000 messages while the actual number of messages in my inbox was
around 13000, by other words it looked as 12000 messages were deleted.
Trying to exit and launch the program again gave different numbers for
messages in the inbox. Eventually the inbox recovered on its own. At
this moment I decided to back up my inbox.dbx file and all others dbx
files on a DVD, format the hard drive and install programs. However
after installing inbox.dbx into outlook express DBXs folder, the
outlook did not recognize it, the inbox is always empty while the
inbox.dbx size is around 690 MB.
I searched the web for recovery programs. I will be honest if I said
that I tried them all. Neither of them gave me back even one message. It
seems that the file is severely corrupted. I tried even many unformat
and undelete tools trying to recover some data, but noway.
I am still keeping the dbx file on my hard drive, hoping that someday
I'll be able to recover it.
Note : the other DBXs were not corrupted and they still work. this
includes: sent items.dbx, deleted items.dbx ......etc

Thank you very much for your interest.
anyway before I send it, I'd like to remind you about the size of the file.
it is of 600 MB or more ...
is it ok with you ??

Instead of just copying the .dbx file into the folder, try importing
the files.  Good luck.

Thank you Whitehathacker
however the repairing applications failed in recovering the messages back. 
you can imagine how the state with importing ...no application
imported any file back too ... anyway thank you for your suggestion...
I still keep the file ... may I recover the messages someday.

Try this programme. It will save all your emails in a specific folder.
Rename the files to .eml then just drag them to your inbox. This is
brilliant and best of all its totally FREE.

http://macallan.club.fr/SETUP/OutLookExpressExtraction.zip

I had a very similar problem and this worked.

Regards

Thank you Gomezzn ...
as I mentioned in the original post ....
I have tried most if not all the available applications on the net
including the program you advised me to try ...
I tried it again .. but with no satisfying results ...
My understnading is that the original DBX file was infected with some
kind of virus that impaired its encryption.
So what I am actually looking for ..some up to date new application
that can reverse the virus effect and knows very precisely what this
virus did to the file.