Xbox 360 Game backups?

If I back up games I buy, keep the orignals, and flash my xbox will it void my warrenty or get me banned from xbox live? All my games are slowly screwing up like in cod4/5 certain maps on some game modes arent readable and on farcry sometimes if i select an item in builder it goes unreadable. Getting annoying and plannign on backing up but I would love some info about the side-effects (banning or voiding warrenty)