Q: I am trying to authorize a new computer but i am at my limit of 5.  Of the 5 units 4 are dead and no longer excist so how do I de-authorize computers that no loger excist?

If your computer doesn't work or you don't have it, you need to deauthorize all computers and then reauthorize the ones you're still using. You don't need to deauthorize your iPhone, iPad, or iPod touch, but you do need to disassociate your iOS devices from your Apple ID. Your iOS devices don’t use any available authorizations.

Deauthorize your computer using iTunes - Apple Support

Use the Deauthorize All command documented in this article, or if it isn't an option, the 'contact iTunes Store support' link at the bottom of it.

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Deauthorize all of your computers and then reauthorize the one(s) you still have. See: Deauthorize your computer using iTunes - Apple Support