First, thanks for joining and thanks for renewing or - so far - trying to renew.
In the vast majority of cases, people's memberships expired (didn't auto-renew) because credit cards were out of date or in a few cases declined. Unfortunately the current system doesn't make it terribly obvious how you change your credit card info. We're working to make that more straightforward. But here's how you do it.
To edit or use a different credit card, first log in at the sign in at the top of the right of the site near the Bookmarks link. When you see 'signed in as xxx', click that pull down menu and go to 'account settings'. Once you're on the accounts settings page, go to the bottom of the menu on the left and click subscription. Then click the button that says "Change Your Subscription Information". That will take you to a page where you can change your credit card information.
Once you've done that, simply renew your subscription.