How to repair bootcamp after partitioning for triple boot

Last time when I tries to partition my Mac, Bootcamp got messed up, what I did is boot into the Windows 10 installer (CD or USB). You can download an ISO here, then burn it to an DVD disc or USB drive. Then pass through the language selection screen, when you get to a screen that says Install Now, there should be a button on the bottom left corner saying Repair This Computer (or something like that, I don't have the CD right now). You should get to a screen similar to this, click Advanced options:

Now click on Startup Repair:

Then follow the instruction to fix startup, then you should be able to boot back into Windows 10.

Hope this help.

P.S. This seems like a problem with the MBR when you partition the drive.

If that can't fix Windows 10 startup, you may be having some problems with the Windows partition.