Are there any other admin accounts? Also have any admin accounts been deleted from SP?
Because SP admins and WP admins are completely different, you can be a WP admin and not an SP admin. If the original SP admin account is deleted and no more were created, then you should be offered access and the capability to create one from WP admins.
Unfortunately also, it is possible to delete the one SP admin if the corresponding WP account is deleted from the WP admin, which if no others are in place will lock you out completely. It’s one of the only WP tasks that can’t be modified so there’s no way we can protect against it so to speak. The fix for this is either a fresh install, or a few database modifications which we can help with of course.
But that’s about it. From searching I don’t think there’s ever been a problem reported regarding being locked out of the SP admin pages that wasn’t to do with a combination of WP v.s SP admins, accounts used or deleted accounts. And that itself is a very rare occurrence.
So, back over to you I’m afraid! Is any of the above a possibility?