How do I permanently stop/cancel an Overtime build?

We are using TeamCity Pro, v.6.5.1, build 17834, and having trouble stopping a continuous integration build that has been running overtime.  It has been attempting to build for 3 days (our typical build time is 1 hour), the warning in TeamCity indicates "This build is probably hanging".  Stopping the build does not work, it just resumes again a few minutes later.  We even tried re-booting the TeamCity server and the build agent servers.  Can anyone advise how I can suspend these builds?

thanks
Wayne