Thunderbird 91.10.0 (32-bit), Windows 11. My PC went to sleep as normal while I was out for a few hours. When I returned and woke it up to check my emails I noticed the Thunderbird Calendar had gone - just the Inbox is there. In the View menu Calendar and Tasks are greyed out. The Calendar is stand-alone on the PC, not synched anywhere. I had put a couple of new Calendar entries in earlier, everything looked fine. No updates, installs or uninstalls before this happened. A Bitdefender scan says my system is clean. Email seems to be working fine. I have reached the limit of my technical abilities, any suggestions please?