There is no TFS specific data stored on the build machine, so from a TFS perspective there is nothing to backup/restore.
To setup a new build machine, just install the TFS build software, and point it to your TFS Collection.
The thing that will take time to reconfigure is any software or SDK's you may have installed on your build server that are required by your build. This has nothing to do with TFS, and is difficult to backup and restore to a different machine.
One option is to use a P2V tool to convert your physical machine to a VM, then you can move it to any host.
Otherwise, you are probably looking at just rebuilding a build server and redoing the installs necessary. This time be sure to do it in a VM so you can easily move it around between hardware in the future.