Hi William, a few questions to help the Support devs help you:
What was the original OS ?
Where is your music library stored ? What file system does it use ? Can Windows 10 see it ?
When Windows 10 started, did it identify any other library and give you a choice between controlling that library or this computer ? If so, which did you select ?
Were you ever asked to authorise a new computer for your licence ? If so, how did you respond ?
It may also be helpful if you could briefly describe the other components in your system and network..
Those things should help get this fixed quickly for you.