I realize it's a major PITA, but at some point... the lesser of two evils is to re-install the OS and all apps/plugins. If you know the audio interface is fine, that's the most logical/sensible solution. Yes, you'll spend several days getting the machine loaded... but it's better than spinning your wheels.
As was already mentioned, I wouldn't do an upgrade install of Win8.
That may not solve the problem... and you'd waste more time/money.
Once the machine is back up and running, take the time to make an up-to-date backup image file.
That way... you'll avoid situations like this in the future.
If something fouls up the machine, you re-load your backup image file... and you're right back in business.
I'd start by making a backup image file of the existing Win7 install (just in case).
Now, re-install Win7 and the audio interface... and make sure it's working.
If audio behaves as expected, then I'd start the process of installing programs/plugins.