This is the crucial part in your message ...
- "The disk contains an unclean file system"
- "The NTFS partition is in an unsafe state"
Remember... windows discs need to be checked for filesystem problems.
You can try to fix this from Ubuntu with
ntfsprogs. If not installed ...
sudo apt-get install ntfsprogs
and this will try to clean the disc ...
sudo ntfsfix /dev/sda3
ntfsfix is a utility that fixes some common NTFS problems. ntfsfix is NOT a Linux version of chkdsk. It only repairs some fundamental NTFS inconsistencies, resets the NTFS journal file and schedules an NTFS consistency check for the first boot into Windows.
You may run
ntfsfix on an NTFS volume if you think it was damaged by Windows or some other way and it cannot be mounted.
- You can also follow the last remark: mount the disc in readonly. You can then extract the contents to another disc.
- If the disc do not have anything important you can also format them and ditch ntfs altogether.
I also found this on the ntfs-3g page and is probably important too since it has the exact same message (caveat: the solution requires a working Windows 8...):
"Metadata kept in Windows cache, refused to mount"
When dual booting with Windows 8, trying to mount a partition that is visible to Windows may yield the following error:
The disk contains an unclean file system (0, 0).
Metadata kept in Windows cache, refused to mount.
Failed to mount '/dev/sdc1': Operation not permitted
The NTFS partition is in an unsafe state. Please resume and shutdown
Windows fully (no hibernation or fast restarting), or mount the volume
read-only with the 'ro' mount option.
The problem is due to the new Windows 8 feature called "fast startup". When fast startup is enabled, part of the metadata of all mounted partitions are restored to the state they were at the previous closing down. As a consequence, changes made on Linux may be lost. This can happen on any partition of an internal disk when leaving Windows 8 by selecting "Shut down" or "Hibernate". Leaving Windows 8 by selecting "Restart", however, is apparently safe.
To enable writing to the partitions on other operating systems, be sure the fast restarting of Windows 8 is disabled. This can be achieved by issuing as an administrator the command:
powercfg /h off
You can check the current settings on Control Panel > Hardware and Sound > Power Options > System Setting > Choose what the power buttons do. The box "Turn on fast startup" should either be disabled or missing.
Best course of action: re-install Windows 8. Fix the problem with the disc. Install Ubuntu.