Well, I think I solved the problem, even though I'm not very happy about it. I knew it had to be connected to Google +, which my account was, but apparently, I can't go to YouTube.com and leave comments; I have to connect to Google's website (on YouTube, I click the arrow that leads to my account options, and then I have to click on "Google+"), and then I can comment, but the site changes to plus.google.com. If I stay on YouTube, a comment box will pop up, and it even shows the profile pic I just added, but it won't show any of the letters I'm typing. This really miffs me! I shouldn't have to connect to another site just to comment on videos I can see when at the main site (YouTube.com, I mean, as opposed to plus.google.com). Yeesh!