El Capitan has deleted my bootcamp windows partition
I upgraded to El Capitan and now my Windows 10 partition has disappeared. After googling the problem, it seems to be related to having resized my windows partition - which I did when I upgraded to Windows 10, after upgrading to Yosemite but before upgrading to El Capitan... I attach the following screen-shot which seems to be the first of the questions that gets asked:
I also tried to install gdisk 1.0.0 but I get a warning message when I do. I tried ignoring the message and installing anyway, but it seems to fail to install.
Any help would be greatly appreciated as I don't think I can face having to reinstall everything from scratch.
iMac, OS X El Capitan (10.11), Windows 10 boot camp partition