Recovering Win7 Image to New PC Running Win 8.1

My 8-yr old PC (Win7) recently died; total HDD failure.  I had been making regular image backups on an ext backup drive using NG15.  I just bought a new replacement PC with Win 8.1, and I need some expert guidance on how best to recover my backed-up image/data from the ext backup drive and load it to my new PC.  I can see a recent backup image file on the ext drive.  My first concern is whether a technical problem may already exist with the backup image being based on Win7 vs my new PC running on Win 8.1?

I was able to install NG15 on the new PC, but it will not accept the old product key, so I’m able to use NG for only the next 30 days.  I read elsewhere on the forum that NG won’t activate if installed on anything newer than Win7.  

Thanks in advance for your help in solving this puzzle.