Why do my games in ipod delete by itself!!!!

Hello,
i have a problem with my ipod touch i was syncing my songs when suddenly some of the game started deleting themselves but i have alot of space so its nt a space issue it jus deleted everytime i sync a song frm my pc the games end up deleting an di have to install them again why is this so ? pls help and how can u recover them where do you go on itunes to see all the deleted games?