To add to what @Just £isa Now! said, unfortunately ProSeries no longer has those codes from prior years.
So there is no 'access' to year 2000 for those who did not already have it installed because there is no code available to unlock it.
If it was previously installed and somethine along the lines of a Windows update removes your code, ProSeries is unable to get you back into the program because it requires the code, just as it would with someone who did not have it previously installed.
I do hope this helps clarify.