Problems with iTunes

I"ve never liked iTunes, always prefered Windows Media Player....and a recent problem I've had is the reason why.  last weekend I downloaded an updated version not thinking there would be any problems.  But when it finally finished probably 80% of my purchased music of various OSTs and random tracks for the whole albums....were gone.  I'd get an error messaage that would say "the original track [insert name] can not be found.  Locate it?"   And that has happened with every OST I have from Ghost to Tomb Raider to even the most recent Outlaws OST.  I have even tried re-downloading each album and recovering/refreshing the tracks that way but nothing works permanently.