Where who ever infected the system wants money to allow you to read your data again.
No easy answer as most of this type of attack has succeed when this happens and any remedial work is so much harder if not impossible to recover data.
Ideally you would wipe the HDD with something like Boot & Nuke then install the OS and set up some security and AV Product before you then pick-up your Backup whatever and return your data to the drive. It is far easier to blow everything away then try to rebuild every time.
However I doubt that you have backed up any of your data so you’ll have to search the internet on a different computer or at least the one you have infected but after removing the HDD fitting another one and loading the OS to that and then with the Infected drive in a Dock or USB Cable scan it till it either destroys all the data on the drive or rebuilds the data.