Dell Precision 470 problems with Windows 7 usig 4GB RAM modules

Hi,

I have a Dell Precision 470 computer (7 actually) and I have been trying to upgrade the ram to the maximum 4GB modules that are suppose to be compatable with this machine. I have no problem with using x4 4GB 2Rx4 DDR2-400 PC2-3200R ECC Registered modules when running the computer in XP; but when I try running Windows 7 the screen has blacked out areas and the colors are not displaying correctly. This is further made strange by the fact that Windows 7 boots fine and the colors look perfect up until it reaches the desktop which is where the trouble begins.

After several trial and errors, I'm at a loss as to why they don't work and would appreciate some feedback from others, hopefully from those who have faced this problem and found a solution.

Before you make a quick response, please understand the following:
* This computer accepts up to 16GB of memory per Dell specs
* I have memory fan installed

In my trial and errors I have used both single and dual rank module from 512KB, 1GB, 2GB, and 4GB capacities. They are all DDR2-400 PC2-3200R ECC Registered.

I currently have one computer working with x2 2GB single rank and x2 2GB dual rank modules, no issues. I can also use only 1 4GB module and (althought the computer doesn't like it) it boots to the desktop and works just fine. It's only when I put more than 1 4GB module in that I have problems.

NOTE: The 4GB modules are a MATCHING set. So it is not a RAM compatibility issue.

Any insight or help into solving this problem would be appreciated. Thanks.