Syncing iphone without erasing everything?

Ok so my dad for some reason wiped our whole computer to put windows 7 on it. And so my whole itunes librairy is gone. I want to add new music but its making me erase and sync. I have over 2000 songs on my iphone and most of it is downloaded off of datpiff (all legal) which means I would have to individually download over 100 albums individually again which is a pain in my ***.Is there anyway to get around this?

Start doing manual instead of sync entire library.

It should NOT erase anything