Hey rolliegul,
It sounds as if you are attempting to authorize your MacBook for use with an iTunes account, but already have 5 computers authorized on that account. You have attempted to "Deauthorize All" of your computers but have been told that this may only be done once per year. Is that correct?
In order to authorize the new MacBook you will need to deauthorize at least one of the other computers. You mention that one of the older computers is out of commission, so you can't do anything with that except to "Deauthorize all" but you can deauthorize a different computer. This article explains how to do so - Deauthorize your computer using iTunes. In particular see the section titled Deauthorize one computer.
Once one year has passed since the last time Deauthorize All was used, you will be able to use it again so that you can deauthorize the computer that is no longer working. See the section of the above article titled Deauthorize all computers.
Having deathorized all computers you will then need to reauthorize each computer you intend to continue to use with the iTunes account. See the section of the above article titled After you deauthorize.
Thanks for using Apple Support Communities.
Happy computing.