Windows 7 64 bit won't recognize 8 G RAM

The old chips are DDR3 1066mhz

The new chips are DDR3-1600(PC3-12800) Non ECC Unbuffered 240 pin = 1.5 CL=11 Memory
4allmemory # 7777050.

I should mention that I also tried just (1) of the old chips and the machine booted fine... I then removed that chip and then tried just (1) of the new chips... in the same slot.  Black screen again.

According to the spec sheet that web_tracker posted, 1333 is the max frequency supported by that machine.

Good observation.  I will contact 4allmemory accordingly.

Will I be able to use the original 1066 chips with 1333 chips, or should I make sure the new ones are 1066 as well?

As I understand, the higher-speed chips will be underclocked down to the slower speed. Wait for someone else to confirm, though.

I am not sure if these sticks will work due to the max MHz has been exceeded the recommended mhz. Contact Dell to find out for sure if this is the problem.

Many websites do say that you can run a higher speed ram module in your system but it will run at the maximum speed of the mobo. I was going to say there is an issue with the two speeds of memory you are using but, you tried the new memory in the slots with the old memory removed. Puzzling indeed. It is highly unlikely both new modules would be bad, but then it is not impossible. Do you have another mobo where you can test these sticks of memory? Other than that you need to contact the person where you got these sticks and ask for an exchange.

I am not sure if these sticks will work due to the max MHz has been exceeded the recommended mhz.

Agreed. But I am saying that if you decide to buy 1333 sticks, they will be underclocked (by the system) to 1066 to match the existing sticks frequency.

I contacted 4allmemory and ordered replacements at 1066.

Will have them tomorrow.... and will update the status of this request.

Thanks for the quick responses.

Will also check the BIOS settings for the voltage... if we can use the first batch of new chips, fine, if not, we will try the incoming new batch.

Some progress. The (2) 4G chips rated 1066 mhz arrived. After putting them, bootup proceeded through the "System memory has changed" screen... and the chips are shown properly in the BIOS that lists slot and capacity.

However, after that I get the:

Windows failed to start properly - continue normally - or run windows repair.  Both options kick me back to a reboot and the same "Windows failed to start properly" screen.

Dumb question... would the motherboard be using different chip set drivers when a 32 bit os is installed, vs 64 bit os.   (The prior XP OS was 32bit.)?  I don't know if that is an issue, but I am going to see if I track them down and see if there is a difference.

For XP, Dell always required installing the chipset drivers after the XP OS was installed.  Don't know if that applies to W7.

yes - it applies also.
afyer installing any OS you have to install ALL drivers for it.
in many cases, windows will install generic drivers - but it can be wise to update them all

"... would the motherboard be using different chip set drivers when a 32 bit os is installed, vs 64 bit os.  " ==>  The motherboard doesn't "use" chipset drivers ... the installed OS needs the drivers to properly "talk" to the motherboard's chipset.    Most manufacturers have a unified chipset driver that runs on either 32 or 64 bit OS's ... and for older hardware Windows 7 likely already "knows" about you chipset anyway - it certainly has drivers built-in to the installer for the Q45 chipset in your system.   You can install Intel's

It wouldn't hurt to download Intel's unified chipset installer for the Q45 (available at either Intel or Dell's sites) ... but that's NOT your problem here.

From your experience so far, it's likely there's an issue besides just your new memory modules.    You may have a corrupt install [You could try re-installing Windows 7 using a different installer disk);   your motherboard may have issues [Look VERY carefully at all of the capacitors to ensure there are no signs of leakage or bulging ... this is a common problem and would easily cause issues like you're seeing];  and you may simply have a very marginal power supply that the added load of additional memory has put "over the edge"  [Trying a known-good higher-power PSU would easily confirm if that's an issue].

The fact your other modules didn't show up correctly also tends to point to a potential hardware issue, as there shouldn't have been any problem with them either.

Had my hands back on the computer again.

This time I took (2) 2GB chips out of another Optiplex 780 that had (4) installed. Let call this machine B.

Put these (2) into the problem machine (machine A) and after the usual "system memory has changed" message... it booted fine.  This was with a total of (4) 2G chips.

I then tried adding the (2) 4G chips to the machine B... and although it gave me a "system memory has changed" message... it would not boot.

Something about the combination of hardware on the optiplex 780 (2 different machines) just does not like the 4G chips... even though both crucial and 4all memory recommend them.

I did check the state of the capacitors on the mother board of B... no oozing out the top... I have seen that on other machines that have died... but this one looks fine.

I am going to order additional 2G chips for machine A and call it done.

Thanks very much for all the comments and suggestions. This was really an odd one. Will be splitting the points.

Really strange.

I just had one other thought => check the BIOS to see if there is an "Install Mode".    This is a mode that was common on Dell servers a few years ago when there were problems installing some OS's with "too much" memory.   What it does is limit the total memory capability.   I doubt that's your issue -- but it certainly wouldn't hurt to double-check.   If you find it, turn it off.

I tend to think this is a limitation on the machine, it is possible that Dell gave the memory companies miss information stating that the slots would accept four gb sticks when they only recognize 2gb. Thanks for being fair when awarding the points.

You are welcome.  Four people all made suggestions that would help under normal circumstances... so I did a four way split.