Try this:
Open the file in WinRAR (download from internet if you don't have one).
Press your right mouse-button.
Click on "Repair archive", or press Alt+R.
Click on Browse button and select a folder where you want to keep the repaired archive.
There will be two options ("Treat the corrupt archive as RAR" and "Treat the corrupt archive as ZIP".
Select any one of your choice (or see which one will work) and click on OK button.
Go to the folder where you have kept the rar repair and open it (Repaired archive will be named as rebuilt.*.rar or rebuilt.*.zip, where * is the name of original archive).

https://in.answers.yahoo.com/question/index?qid=20120413024756AAkXcMu
http://www.winrar.repair/