iTunes has lost all my APP purchases and reset my library and playlists.

Well as above. I dont have any other username accounts. iTunes has had a breakdown and misplaced my entire library which is on my external hard drive, I havent lost the somgs just the location and all the metadata pertaining to it. Its a pain to reinstate it all but the most worrying part is that all of my APP purchases which I kept stored on iTunes are missing, which is a n awful lot of cash as they are mostly quite expensive music production and photography and film apps. How can I recover my metadata for iTunes and how do I restore all my APP purchases?