Bootcamp windows 8.1 not booting
That’s most likely not related to Mac OS or Bootcamp, but rather a Windows issue. There’s barely enough information from your side to estimate what’s the problem here, but most likely it’s an issue with the windows bootloader. From a Windows install disk or USB stick, open up a command prompt, and execute the commands bootrec.exe /fixmbr and bootrec.exe /fixboot. These should reinstall the bootloader.

In case that doesn’t work, it’s most likely an issue with your Windows installation. Since Windows isn‘t as repairable as Mac or Linux is, it’s likely that reinstalling windows (save all data, format the partition from disk utility in Mac OS and install from the Windows install media again, as you did in the first place) is the best bet to go.

Anyways, since your question is most likely not related to Apple, you’re good to ask in a Windows QA site like superuser.com how to fix your Windows boot (there’ a lot of answered questions already so just search).