Invalid password after Sage 50 essentials auto-update upgrade and then following computer crash during data conversion to new upgrade version.

Sage 50 essentials just asked to auto update. I allowed and selected Upgrade instead of separate install. Then when installed, it needed to convert data. However, computer crashed during this. After some hassle and a Windows 10 massive and long winded upgrade later, I went to start Sage 50 Essentials. This time, 'password is invalid' and I can't get into Sage at all. Any ideas?? Note: I haven't changed the password, just done the upgrade. Thanks in advance for any help given :)