I haven't used PC Basecamp for a year. I had many tracks saved on it last year. Now the're gone and I cannot sign in. What's wrong please?

By the way, I have a 64st.

No need to sign in to use BaseCamp.  Did you update BaseCamp?  If so I suspect it's looking at a different database and BC databases don't just get deleted unless you've deleted them.  Do a search for AllData.gdb.  Once you locate it/them that will show you which folders contain BaseCamp databases.  You need to point BaseCamp at the one created a year or so ago.

If I'm being stupid, please tell me what I'm doing wrong or forgetting. I only used Basecamp  for a trekking trip I planned in Norway last year, so it's possible I'm forgetting what to do. I had maps, routes, etc. loaded. I haven't updated it.

I did install a new hard drive in my PC though.

Is that on my hard drive? I DID backup my hard drive. But obviously, my Basecamp was then back to its raw installed state when I reinstalled it today.

Okay. Looked everywhere. Including on backups before hard drive failed. Don't suppose this AllData.gdb file is saved online on a server, is it? Last hope, probably. :/

Afraid not, if it was on your previous drive it's gone.