Windows partition missing from bootcamp.

I haven't been on my Windows partition in a couple of weeks and when I went to login to it today through the startup screen it was not visible. I can't think of anything that I've done that would cause a major change in the system and partitions. In the disk utility it now appears as 'disk0s4' and is unrepairable and I can't access the files through Finder.

Is this partition recoverable and, if so, how do I go about doing so? Please help. Thanks in advance.