After Googling the issue, I have the following thoughts...
First to parrot other suggestions, ALWAYS WORK USING A COPY OF THE FILE!
 
There was a utility with Clipper called DBU (DBU.exe) that would open DBF files and you could see the structure.  It was pretty easy to use.  Not sure where you would get that today...
 
Step 1.  Make Copy!
Step 2.   Try DBU.exe, or any/all of the things above...
 
Also try this, open a copy of a working DBF in a hex editor.
Then open a copy of the bad DBF in the same hex editor.
 
Compare the information in the first few lines...  I typically don't hex edit files, but this may be the way you need to fix this issue.
 
You can use these as a guide:
http://www.dbf2002.com/dbf-file-format.html
http://www.digitalpreservation.gov/formats/fdd/fdd000325.shtml
 
Look at this:
http://www.bleepingcomputer.com/forums/t/625451/not-a-valid-dbase-table/
 
Here is .NET code to directly read dbf file into data table...If you are into programming...
http://www.codeproject.com/Articles/24247/Load-a-DBF-into-a-DataTable
http://dbasereader.codeplex.com/
 
Do not know how reputable these are but:
https://dbf.recoverytoolbox.com/
 
https://www.repairtoolbox.com/dbfrepair.html
 
 
Hope this in some small way helps...I have been there :(
 

 how many methods to get back dbf file, a lot of thanks.

unormands36
 
I have Dbase PLUS 10, it is quite old, but before today it worked reliable, but several days ago at opening .dbf file I got: Not a valid dBASE table. I need to repair dbf, any suggestions...

It is very old-fashioned program dude, but several years ago, I had similar trouble.
 
Not many methods can solve this error.
 
But there is an instrument like DBF files Online repair service, it was created for fastest and reliable restoration of .dbf files, for me it is the most effective.

Dude, you got me great solution, I am very appreciated to you!