Brand New Computer / Brand New DDJ SB Controller and Serato Dj / Nothing works / I tunes will not played imported purchases and controller wont play itunes / Please HELP

I just bought alot of equipment for alot of money and I cant figure this out. I am by no means a slouch on the computer but why when we pay so much money does this have to be so complicated to get going. Anyways Itunes will not play any of the songs i redownloaded from my purchased stuff. It shows it on my library but when I ask to play a song i get nothing. Took awhile to DL my 2000 or so purchases but im at my wits end. Can somebody help please?