I don't have access to the five previous computers I have authorized on itunes, so how do I deauthorize them?

You will have to deauthorize all of your computers and then re-authorize the ones that you want to be authorized now. You can do this in your account section of iTunes or Music.

Here is a link to the Apple support article with step-by-step instructions:

Authorize or deauthorize your computer for iTunes Store purchases - Apple Support

Scroll down to the section labeled “If you need to deauthorize a computer that you don't have access to”.

gagebaron wrote:

I can't open itunes on this computer, because I have to deauthorize the other computers;

I don't believe that is correct.

You can install iTunes on as many computers as you wish. What you cannot do is authorise more than five computers that can download your iTunes Store purchases.

The first thing to do therefore is work out why you cannot open iTunes on your current computer. What happens when you try to open iTunes, what error messages do you see?

Once you resolve the issue of iTunes not opening (and only then), you can then go to your account in the iTunes Store and use the De-authorise All option to de-authorise all your computers, whether you have access to them or not. Then you authorise the computers that you do want.

You can still OPEN iTunes or Music and sign in to your account, even if you can’t authorize the computer you’re doing it from. Authorizing a computer allows you to play your iTunes Store purchases, it does not allow/disallow access to the app itself.

Yes, you CAN still sign into your account in iTunes even if the computer you’re doing it from is not authorized. Again, authorizing a computer only allows it to download/play purchased content - it does NOT prevent access to the app or your account.

If you are unable to OPEN iTunes or sign in to your account, then you have a different problem that is not related to authorization.

gagebaron wrote:

I cannot log into iTunes, because I already have five other computers authorized.

As both myself and Wengro have told you, that simply is not the case.

Authorisation concerns the ability to download and play music that you have purchased from the iTunes Store and is a step taken after signing into the store.

Please provide precise wording of any error messages that you see when you try to sign into the store, or more detail about what happens when you try, rather than making assumptions about what you think is the cause.

gagebaron wrote:

I haven’t installed, but I can’t login.

I don't understand what you mean. Have you, or have you not installed iTunes? In your first post you did state that:

I'm trying to put itunes on my PC, but it says I've already authorized 5 computers.

If you have not installed iTunes, then that is the issue to be addressed, not authorisation.

It has always been the case that if you no longer have access to a computer that you wish to de-authorise, then you use iTunes to De-authorise All (computers) in your account and then Authorise the computers that you do have. However, there is a limit to the number of times per year that you can do this. Is it this limit that you have reached? If so, there should be a specific message telling you that you have reached the limit of your de-authorisation requests. Again, what is the precise wording of any messages that you see?