Ok. Your TV has a defective DLP chip. If you've ever seen the Texas Instruments commercial for DLP that says "it's the mirrors" this is the part they're talking about.

The DLP chip contains 2 million hinge-mounted mirrors; each one about 0.0008" wide. The mirrors can tilt toward the projection lamp (mirror is "on") which creates a bright pixel on the display; or away from it (mirror is "off") which creates a dark pixel.

The dot you're seeing is a stuck mirror. Your white dot is a mirror that's stuck "on" (facing the lamp). This is very common. Eventually, you'll get more. You may even get some black dots (stuck facing away from the lamp). Unfortunately, they'll eventually cover the entire screen like this.

So, what now? You should start by calling Mitsubishi because they might repair this for free, even if you're outside the warranty period (this is a very common issue!).

If they won’t help and you want to have this repaired, you should contact a qualified technician… this is not an easy job and will require significant disassembly.

If you really want to do this yourself, let me know. I can send you the part numbers, pricing, etc. I'll warn you, though... there are no guarantees this won't happen again. You might want to look into replacing the TV. This is a big reason DLPs really aren't made anymore.

If you'd like clarification or have more questions for me, click "Reply to expert." If you're finished, please rate me highly so I get credit for helping you. Without your rating, I'm not compensated for my time here. Rating me will not close your question.

Best,
Dan