Yip Pottypete has it spot on - dots on screen or any kind of artifact are generally associated with graphic firmware (onboard or discrete cards) and the software (Drivers). Set fail safe defaults in your bios, boot into your OS in safe mode. Remove all graphic drivers, and all traces of graphic registry entries. Then reset and install the latest drivers for your graphic solution.
The one thing that does worry me is the fact that you did a install of a different OS and still you had the problem. The only time that can happen is if you do not do a fresh install, in other words used the upgrade option when installing Win7. Which you did not do.
Quick question what could you possibly have done to your ram that was incorrect. Bios settings for ram are quite simple really, either they work and the Motherboard boots up or they do not work and the board does not and needs to be reset. Just interested on that score.
One last thing to try - sure you have tried this already - disconnect all hardware and all power connectors so that you are left with a pretty bare motherboard. Then remove the cmos battery and reset the cmos. It will show you how to do thin in the manual - involves changing pin settings on the jumbers. Leave the battery out for an hour or so and then plug everything back in. Set to default and see if the problem is still there.