Hi Steve
Is your existing 'installation' in your 'Program Files' folder?
If so TDL might have detected that it can no longer save files to this folder under Windows 10 and will have created a new ini file in 'C:\Users\<user>\AppData\Roaming\Abstractspoon\ToDoList'.
If you find this to be correct, try copying your previous ini file to this location (I'll implement a fix in 7.1 to attempt this automatically).
If this is not correct, you could try
installing the Alpha of 7.1 to a similar location and then checking 'Help > About' as this now reports (at the bottom of the dialog) where the ini is located.