Cannot Boot to BootCamp

I've not used BootCamp for a while now, and I've been using my external (Mac) boot disk a lot lately, and I tried to go into BootCamp today, and got a black screen saying "No bootable device -- insert boot disk and press any key"... Is there any way I can repair this without deleting the Windows partition?

Just to clarify, the Windows partition had been working perfectly for ages, but hasn't been in use for a couple of months.

 

All I get when I hold the Option key is Macintosh HD, my internal Mac boot disk, and Recovery HD, the internal recovery disk... Not very useful haha

--- Post Merged, Aug 1, 2016 ---

Something is telling me there's something wrong with the partition map, as it takes a long time after choosing Bootcamp in Recovery as the startup disk for the error to appear... just a guess though...

 

I've used "hold option when booting from off", "boot to recovery and use startup disk selector" and "startup disk selector in System Preferences", however the first method no longer shows Windows as an option to booth to, just Macintosh HD and Recovery 10.12

--- Post Merged, Aug 1, 2016 ---

Yes it does, I can mount and unmount it too.
No I'm not - I did have it turned on but I've turned it off since then.
My core storage setup has been the same since I installed Windows many months ago. Macintosh HD partition has been erased a few times and reinstalled, whilst Windows had been working perfectly.

 

Windows 10, and I installed from an ISO image, so there is no Windows installed CD in sight...

 

I've reinstalled the Windows support software onto my USB stick from Bootcamp Assistant, I'll try using that and see what happens...

 

After having my whole system crash multiple times in a row, I gave up, and erased the whole disk... The entire thing is fully broken... Should be getting an SSD very soon though, which should help smoothen things out