iTunes is corrupted can't reinstall.
For some reason my iTunes, which came with my Mac, has become corrupted. I've tried reinstalling it by downloading from the App Store but it cannot be recognised and when checking on the info it says zero bytes on the disk (image).
I've searched on the Apple support communities but cannot find an answer to this question. Can anyone tell me how I can go about replacing this corrupted iTunes?
Thank you.
iMac, OS X Mountain Lion (10.8.5)