Cannot create bootcamp partition?

I just reinstalled OS X Yosemite because for some reason I couldn't delete the bootcamp partition free space. The only way was to reinstall it, which I did. Now that Im trying to make a new bootcamp partition with Windows 8.1 ISO downloaded from the microsoft website, It won't work. it gives me the error 'disk could not be partitioned'. I've already tried the login to single user mode and the sbin/fsck -fy code, and it doesn't work. Any ideas? This is driving me crazy.