I switched computers and am having trouble

I switched computers from my grandmas to my houses. When using my grandmas i had a ipod nano 6th gen but it broke so i didnt use anything for about a half year. Now i have a 3rd gen nano and im trying to get this all going. I signed on and downloaded itunes to ths computer and everything fine but when i try to look at my library, i cant see any of My 800+ songs except for the few songs that ive perchused. i also plugged in my 3rd gen nano into the computer and it didnt do anything and now its frozen and wont respond. i hope its not broken. any advise would be great. and if you need any more detailes just let me know.