Downloading Sibelius software

I bought a 13' Macbook Air 20 just before Christmas & have discovered that I can't access my Sibelius software. Avid say that the Mac is incompatible with the software. I have Sibelius files which I'd worked on for 6 months & can't access them to print, or modify. HELP! Short of buying an old laptop to use the files, what can I do?