I guess that most of the students are still learning their speech on their computer/phone while you are delivering yours. Add to that the fact that most of them aren't here to learn but just to get good grades and you get a class almost full of people who don't really care what you have to say.
Its a bit of pity really . You kind of want them to learn on the subject you're talking about.
You can't teach them if they don't want to learn. Take this from a guy who's been burned too many times trying to "fix" others by "making 'em learn". I first wanted to write a whole comment about how I did my presentations, but decided to go for something more concise. If the speech is something you have to do for a mark of any sort, enjoy doing it for your own sake. Have fun talking about what you like, and find something to like in whatever it is you work with. If you're passionate about the subject, you'll certainly enjoy presenting it to others: just think of it as reading a lecture to a group of friends and share your passion with them. You won't lift their eyes off the screens with wishful thinking, but your emotional charge may do just that without you even trying. Can't give you an advice on doing speeches of your own volition - never did one myself - but I imagine it's not far off. Instead of "making them learn", make them want to learn by showing them what there is to learn. "Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime".