If the listing is current and indexed, you can search by item number by entering the number directly into the search bar. Just paste your own item number of those digits at the end of the page address. That will work even if the listing has ended within ninety days or if it is not yet indexed.

You can search for Sellers via the Advanced link to the right of the eBay Search window. Scroll down to the Seller section and enter the ID and complete the Search at the top or bottom of the page.

When was the last time you used the old account? eBay does purge accounts after a long period of inactivity - they send you an annual reminder to login to verify your info so your account remains active. If your account was purged, there is no way to get it back.