Well, you need to start simple. Instead of trying to force the UPnP service to index an even bigger volume (1.6TB!), start with setting UPnP to index a folder with just one video, one music file and one photo. Hit refresh, wait for it to show up on the 360, test that all three are able to be seen and viewed/played.
Now, start adding a bunch of video files, say, that're the same codec/container as the one that you got working, refresh/rebuild the index, test them on the 360, and so on.
Basically sounds like you've got some kind of file that the UPnP service hangs up on when trying to index, so you need to figure out what that is. The UPnP service is apparently not sophisticated enough to handle indexing certain types of files and, rather than just skip over them and output the error to a log file, it just hangs up or causes other problems.