Are you viewing it "Flat" or "Nested"?  You need to view the larger threads as "Flat" or the computer explodes trying to load them.   It's at the top right hand side of the threads...a drop down menu.  You can also change your default in your settings somewhere.

I hate viewing them that way because you can't tell who replied to what thread, but it's the only way to view large threads so I now see all of mine that way.