Windows 7: W7 x64 doesn't like 4GB of ram...

So I can use any of the 2GB sticks in slot one or two, but I can't use both (memory is Crucial XMS2 TWIN2X4096-6400C5C, DDR2-800).

The moment I start trying to use both, Windows 7 will start giving me "Windows Explorer has crashed" app errors for explorer.exe. Ran memtest on each stick and had no errors. Then ran each separately in slot 1 and then in slot 2. No problems.

This is a fresh install of Windows 7 on a clean drive and the error has occured since first boot.

The only things I've loaded are the motherboard's drivers (motherboard is the MSI 785GTM-E45 with stock settings), Nvidia drivers for the 9800GTX+, Nero 9, and the onboard Realtek HD Audio. No matter what, the computer will run just fine on 2GB, but not 4GB. Think any of these could have an issue with 4GB?

Using these variables, I've ruled out the following potential issues:
-Bad RAM (did Memtest86 off of bootable disc)
-Bad mobo RAM slots (tested RAM, ran good RAM sticks in both slots individually)
-Driver conflict (could still be an issue I suppose)
-Please do not tell me it's a context menu issue because it is not (fresh install, nothing added)
-BIOS shouldn't be an issue since the computer runs with 4GB when Windows 7 is not running. The issue is in Windows 7 ONLY (checked, newest)

Thanks in advance.

Equipment links (newegg):
RAM: http://www.newegg.com/Product/Produc...82E16820145241
Mobo: http://www.newegg.com/Product/Produc...Tpk=785gtm-e45
CPU: http://www.newegg.com/Product/Produc...-680-_-Product

Has it given you a BSOD??

That's a negative. No BSODs at all.

Call me crazy, but I'm not in agreement that just because another OS can run with 2 slots filled that it can't be a hardware issue. If I were you, I'd be a bit more open-minded about the cause of your problem.

Might be your mainboard BIOS needs a flash update, and it sounds likely that you may not have got your memory settings quite right at BIOS level either.

Are you certain your sticks are sound? Can you swap them out and run Memtest on them individually...

Does your motherboard manufacturer state your board has been tested with that particular physical memory?

Have any suggestions Dave?

Checked for BIOS updates. Have the most current.

Did memtest already. 7-8 passes on each individually. Then 3 passes together. Nada. Should have stated this in OP actually. Forgot it when I had to retype everything.

Yes, MSI states that it has been test with this memory @ 1.8V.

Mm.. running SFC check at the moment but won't have time to check results until later.

If the memory tests fine, and your BIOS is up to date and correctly set, and the DIMMS are approved then perhaps you have a faulty mainboard...

Can you think of any other ways to test for a faulty mainboard besides the method I tried (ran the tested RAM in each slot individually with no issues)?

Thanks guys. I need help jogging my mind with this issue. I'm stumped.

I sure hope it isn't a mainboard issue because I doubt I can return this mobo to Fry's 500 miles away within the required 15 day limit

Try and replicate the results with different DIMMS...

I have a Gigabyte motherboard with 4 DDR slots. I can use 4 512s, 1, 2, or 3 1GB sticks, but not 4. Even with the most current bios, no go. I have a Foxconn motherboard with the same chipset and 4 GB is no problem. Why one and not the other? Who knows?

Cheers!
Robert