i have a load of stuff on my ipad but I can't get it onto my conputer, pressing sync comes up with a message saying it will all be deleted. I've transferred all purchases but this only does the few things I've got from apple (apps and a few itunes) help?

I own an ipad2 and have loads of music and vids/photos etc on it from an old pc.

I just bought a new pc and wanted to transfer everything to the new pc

I've transferred purchases but this only transfers things bought in the itunes store like apps and a few songs

The rest of the content is still on my ipad.

When I press sync, it warns that it will delete all the content on my ipad and replace with the few things I've managed to import.

How do I transfer all the content to the new pc?