I've been trying to download and update all of my apps for both my ipad and iphone to my pc via itunes but every app seems to be corrupted.

I had to reinstall my OS to my HP laptop which resulted me in my having to reinstall itunes, while trying to update my app to my iphone 4s and iPad 3rd gen I've found out that while trying to download all of my previously purchased apps from the App Store are corrupted?????? I need help, and can't find any information to tell me what the problem is. Any help would be greatly appreciated because I'm about ready to toss both devices out the window.