[Loki123]

Translation of the error message ?

I assume it has something to do with mounting error. What happens if you mount it with
$ sudo mount /dev/sdb /mnt
?
Might need to change sdb to the appropriate special device file.

---

And give me the output from

$ sudo fdisk -l

[Loki123]

Seems to me that sda is used up by Mint. Your HDD is 500GB right ?

To me this partition seems to be "fake".

Did you encrypt your disk ? or partition.

[Loki123]

Did you encrypt your HDD ? Your Windows install or Mint ?

And it would help if you set your system to English and post the output from fdisk -l again.

[Loki123]

$ sudo mount /dev/sda2 /mnt

tell me what happens ..
You have 3 partitions on the disk. two for Linux and one extended.

[Loki123]

Like they say. Seems like you have damaged that partition or that you are seeing a fake one that shouldn't exist.

Put your HDD to another computer that has Windows and see if you can mount it (Do not format it)
If not you might try some file recovery to recover the data lost from the Windows install and you will have to re install windows.