Hi
There is a utility in Windows 8 for creating a Disk Image.
It's hidden in the Control Panel and it's called Windows 7 File Recovery for some unknown reason, but it will create a disk image and make a bootable repair disk.
Don't back it up to your C:\ drive, it has to be on a separate partition or drive, or a set of disks (not practical if you have 500 Gigabytes of stuff to back up).
If you don't have a second internal hard drive or partition I'd advise getting an external USB hard drive.
Also back up any data you really don't want to lose, like photos and music to it, in uncompressed format, (just copy the files to the drive) they will be there even if you back up get corrupted.
Personally I use Paragon Backup and Recovery, it's free and it's saved me several times.
Mike