unable to boot from windows

I have an iMac 13.2 running OSX 10.11 El Capitan, I also use windows 8.1 as a secondary OS for some of my games.

The problem is that I wanted to try out the 10.12 Sierra Beta, and partitioned my HDD for triple boot, the Beta worked fine but when I tried to boot on windows, I got a message saying "no operating system found". My data still exists on the bootcamp partition,but I can't seem to boot from windows... Is there any way to fix this problem? I don't want to backup my important files and then re-install everything..