You can not format the partition where windows is installed if you use THIS Windows.
There are several ways to rescue all the data which is important to you:
1. the easiest: try to run Windows in protected mode, connect an external HDD and copy all pics, music, documents etc to this HDD - reinstall windows
2. not too easy: buy a new internal HDD and install a fresh Windows on it. After that you have to choose the correct Windows installation on startup. Copy all your data to the new HDD, format the old Windows partition and use this drive as a storage for your games, music etc.
3. hardcore: Download a Linux distribution, run it from CD, connect an external HDD, copy your data and remove all data from your Windows partition. Reinstall Windows
Personal note:
If you have still access to this system (not completely locked, only a popup with the blabla pay or die blabla) : don't use it to access any protected account like mail, Facebook, online banking etc.
If any anti virus is able to remove this crap: never trust this system. Save your files and reinstall Windows.
Firewalls are useless for such fu*king crap. In most cases Ransomware comes as drive-by download while you are watching websites. Firewalls like ZoneAlarm or the Windows firewall would not detect this shit. You are surfing and all FWs will see it as legit. (Not saying firewalls are useless at all)
Protect your System with an Antivirus. But be aware that this is not a 100% protection. No antivir detects all the crap out there.
Work with limited access and do not use an administrative account for your daily work. This minimizes the damage to your system in most cases. The Windows UAC (User Access Control, the window which pops up when you try to install programs "Blabla install blabla. Click Yes or No") is helpful but not the best protection.
Now call me a smart alack
Such things are may daily work. If someone is interested, I'll open a post with a little more info about me (more than I did in my intro post) in the members area, as there are some things I don't want to post visible to the whole World. And Google.
(Not google but Google, I like google but I hate Google