What you have is the DM module not booting up because there are some capacitors in its power supply that are defective. There is a service bulletin for this. The DM module is a board in the set that is responsible for, among other things, the HDTV over the air tuner.
This is going to be a fairly complicated repair if you're not a tech, and you'll most likely have to call a Mits tech to help you.
I also have to tell you about other potential problems with this set, and they are also caused by defective capacitors, and there is a service bulletin regarding this, too. But there are about two dozen of these capacitors scattered throughout the set, and it's a major pain to work on. Although for any problem caused by a capacitor failure, there are probably only 3 or 4 caps causing that problem, the service bulletin tells the tech to replace all of them, because they will all go bad sooner or later.
The tech may decide to pull the guts of the TV out and take it to the shop to perform this procedure (there's no reason to take the whole TV), and ballpark cost is in the $550 range, unless there is a defect in the DM module not associated with the capacitors. If that's the case, add another $500 for that.
But if I may, I'm going to give you some frank advice.
If you are at all inclined to junk this TV, in my opinion now's the time. This set was a dog from the get go. In addition to this problem, there is another issue with a small mirror inside the light box. It directs light out from the lens and up to the large mirror on the back of the TV. The problem is that this mirror is always "looking up," and is constantly collecting dust. This causes a gradual deterioration of your TV's black level, and before you know it, the picture just looks dull. Ideally this mirror must be cleaned every couple of months to maintain your picture quality.
There are a couple of other bad design flaws in this TV, but the above is certainly enough in my book. Mits used to make great TV's, but ever since their entry into the DLP design (and again, this is my opinion), they haven't made a decent TV. Their current line is a step back in the right direction.
Sorry for the bad news, let me know if you have any other questions, and thanks for using JustAnswer!