Okay, so I tried adding comments from another computer and I think I figured it out.
When you click on where it says the number of comments pertaining to a specific post a text box should pop up for you to type in (called "Post a Comment"). Then, in the drop down next to "comment as," try clicking "Name/URL," enter a name (but not a URL) and see if that works. If you have an account through google or are "following" the blog it might be different...
Good luck!
