This worked for me. Went into Windows Mail/Contacts/Settings/Filter Contacts and found that Recent Contacts was not ticked. Ticked it and my contacts returned. How it got turned off is a mystery as I had never been in this area before. However, this was when I reverted to the 'old' Windows Mail. I have since updated to Outlook without a problem.
Later - I spoke too soon. My contacts did not appear in Outlook when I changed to that. I tried every solution offered by the net but none of them applied to my Tiscali account. In the end I was obliged to revert to the old Mail, write them out by hand, update to Outlook and enter them as New contacts. Total pain.