Everybody misunderstood that.
What do you mean by this:
Can I restore using the backup I made before the upgrade or will I lose all that data
If you have now reinstalled windows clean to the HD - and it is working - then yes, you can restore files
you backed up previously.
If you have not yet reinstalled windows - then copy the SYSTEM hive from the non-booting o/s , zip it and post it up.
It will only take a few minutes.