First of all, you need to remove the ransomware software to at least gain more access to your computer. You can do that by following the steps:
1. Restart your PC to "Safe mode with networking"
2. Run a scan with Malwarebytes and Hitman Pro and remove any ransomware files.
3. Attempt to do a system restore (Provided you have a recent system restore point)
4. If system restore is still inaccessible, as "Boosted1g" mentioned, you should use your windows bootable and attempt a restoration/recovery through there.
If this doesn't work, I do not think there is a way for you to restore your windows. As for file restoration, you could try Shadow Explorer to find the files that you want. Afterward, do a clean Windows install and remember to...