I also sent this problem to Our Engineer and his response is below.
Is there any way I can repair the corrupted files? or am I stuck looking for back up files?
Yes, the file is corrupt.
We have had similar problems in the past. I think it has something to do with keeping files on a network and a thing called a "delayed write". The saving of changes gets out of order and it corrupts the file. Although the data is probably mostly there it screws up the indexing of the database, and because they are relational databases it makes them undecipherable. It's a Microsoft problem, not a Bentley one.
Microstation maintains dgn files as database file. It continuously updates the files with your latest edits, rather than save them only when you exit the file. This overcomes the problem of a crash that loses all your work, but it introduces the problem you are having now.
We seem to have it happen less these days, but our solution to it is to have the server do a four hourly backup, so that if it does happen, you will only lose the last lot of changes on a drawing.
You can turn off automatic saving. In the Workspace->preferences->Operation dialog, the third checkbox is "Automatically save design changes". We have not done this, but I think that if you turn that off it will only save your changes when you leave the file. This may prevent your problem by writing all the information at once, but it may make you manually save every time also.