An email address can only be linked to one iTunes account, if you are creating a new account then you will need to use a different email address with it.
Any content that you bought/downloaded with your old iTunes account will remain tied to that old account - so only that account will be able to authorise its content on a computer's iTunes, re-download items, or download updates to its apps. If you have problems with that account then have you tried contacting iTunes Support about it : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Account Management
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