apple id – App Store signon is unresponsive

I have a MBP from mid 2009 with OSX 10.11.6, El Capitan, and, of course, can’t install further OSXs because of hardware issues.

For a few years I’ve been able to browse the App Store but cannot download because I can no longer signon. The kind of downloads I would want to do are things like 3rd party updates.

When I try to signon and the signon dialog box appears, my Apple Id is ok (if I put a nonsense id I’m immediately informed that the id or pwd is incorrect), but it doesn’t matter what I put for the pwd (I believe I know the correct pwd), when I hit Sign In in the dialogue, the dialogue box resizes and becomes blank except for the spinning (sparse) clock wheel; and after a couple of seconds, the wheel disappears from the dialogue box so it becomes completely blank, and that’s how the window stays, forever; and I have to force quit the app.

The Sign In dialog has a pwd reminder link, “forgot?”: if I hit this with my Apple Id entered, as above, the dialog box immediately resizes, the wheel appears for a couple of seconds, then disappears leaving a blank signon box, as before

If I hit “forgot?” without entering my Apple Id, I’m presented with a dialog box in which I can enter the Id; and when I do and continue, I’m presented with a small dialog box containing the Apple logo, beside which is the bold title “Apple Id”, and below that the message: “Your request could not be completed at this time”; and just below this is an “OK” button. After pressing OK, I can then quit the store without force.

From what happens as described in the preceding paragraph, this is an Apple Id problem – although the ID is recognised, the system doesn’t want to proceed with it – can anyone guess why?