You may want to use either a Linux Live USB or CD to boot on a complete live OS, alternatively, and if you're not interested in installing any Linux distribution, you can download and burn GParted which is a tool to manage partitions and filesystems. On the link provided you can download an standalone ISO, which is a bootable operating system that contains and lets you run said app. The advantages of this are:
- It's bootable. You don't have to have a previously installed OS.
- It runs from a CD or USB stick. Your filesystems won't be in use so you can freely operate on them.
- It's linux based. You don't have to worry about windows permissions.
The same bootable disk contains an small file browser, that would let you mount your filesystems and do your backup to any drive or support you want. It supports the most common filesystem types: NTFS, EXT, HFS, FAT.
Its usage is pretty simple and intuitive, you can find more information on its online help pages.
Update:
Since you are using Windows 8 based system, you may have to disable the Secure Boot or enable the Legacy Boot features on your BIOS in order to boot from the live CD or USB.