Windows 7: Dell XPS 600 reboot loop with 4GB (2x2GB) memory

Had 1x 2GB Kingston 667MHz stick, and decided to buy another one. I should point out that both are fully working and were bought brand new from Amazon. I was forced to reinstall windows (Windows 7 Professional 64-bit) for other reasons, and the installer would get to "Starting Windows" then would restart. Did this as many times as I booted it up. After messing around I took out one stick (took out the old one and just had the new one in) and the installer worked perfectly. Got into windows and shut it down to reinstall the other ram stick. When I booted it up, it did the same reboot loop. Seems like it just doesn't want to take 4GB. BIOS says: Installed Memory: 4.0 GB, Memory Channel Mode: Dual Interleaved. Why won't my XPS 600 boot with 4GB RAM!? It IS a 64-bit OS (had to double check just to make sure)

Did you try individual sticks of memory in the same slot or different slots?

Both sticks are KVR667D2N5/2G?

Yes, both are the same exact model. I tried both stick in the same slot, but it also didn't work when I used slots 1 and 3 for single channel. I know slot 1 works because it's what I use with only one stick. I was using slots 1 & 2, I could try 2 & 4 but I don't think that's the issue. I also have Mac on there and it is able to recognize and use 4GB, I don't think it's a hardware issue.

Is this possible?

Up to 2GB Dual-Channel DDR2 SDRAM (667MHz, 2 or 4 DIMMs)
Up to 2GB Dual-Channel DDR2 SDRAM (533MHz, 2 or 4 DIMMs)

Are you limited to 2 GB?

Dell XPS 600 Product Details | Dell

I doubt that's true because I know it is utilizing 4GB in Mac, and also the BIOS recognizes 4GB. On that page it also says Pentium D (up to 3.0GHz), and mine's 3.4GHz. It doesn't make any sense why it IS recognizing 4GB RAM but the 64-bit OS rejects it. It seems that it should AT LEAST say 4GB installed (2GB useable). Is there any way to do a verbose mode in Windows so I can see what exactly is going on? When I go to boot options after failing to start, it says something on the lines of "Windows was previously unable to start up, this could have been caused by a hardware issue".

Documentation
Hi jhohisel
The link above is to your XPS 600 manual it says you can run upto 2GB or 8GB of ram max,
So you are not stuck at 2GB.
But my thinking on reading your manual it does not say you can run 4GB ,
So that may be the problem you have.
Good Luck

On a Dell normally to run dual channel you use slots 1 and 3, they should be color coded, you might want to go over to Crucial.com and run the memory checker and it will tell you exactly what your comp can take. Matched pairs is the only way to go.

Okay, the reason the above site said max 2GB was b/c it was max 2GB per slot. Very confusing.

So there are two white and two black slots. Fill the white first, which is there the two 2GB sticks should go.

That's what I did, heres the layout.
W B W B
|1|3|2|4|
-X---X---
(Where 1 is closest to the CPU)
I filled the white first starting with closest to the CPU. X = Filled, W = White, B = Black. I just ran updates, maybe the update fixed something, I'll put the stick back in and get back. My disk had Win 7 Professional SP1 x64 to be exact.

So I put the new stick in and decided to pull the battery and unplug the power to reset the BIOS. Did that and it reset, but when it got the the "Starting Windows" screen on cue it restarted.