Hello and sorry you're having problems. This is a failure of the "DLP Chip" in the TV- which contains thousands of tiny mirrors that each represent a pixel on the screen. This is a common failure with DLP sets (they all use the same Texas Instruments chip), and the dots on the screen are the tiny mirrors falling off the chip.
In order to correct this, the DLP chip needs to be replaced. If you are a DIY type you can replace this yourself, and the chip can be purchased at the link below for $185:
There is also a video at the link below that shows you how to replace the chip yourself (the TV needs to be partially dismantled to perform this repair):
If this is something you're not comfortable with, then a shop will charge close to $400 parts and labor to replace the chip in your set and can be located at the following link:
Other than that, I'm sorry for the bad news and wish there were a quick fix.
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