Make sure you have the latest BIOS for your system.  If you do not, update it.

If you do, and the RAM doesn't work, it's either faulty or incompatible.  For a good source of guaranteed-compatible RAM:  www.crucial.com

How and where do I find the latest BIOS for my system?

Go to the Dell Support on the home page and click on drivers and downloads. Enter your service tag which you will find on the base of your D600 on the small white sticker. It will list all the latest drivers and BIOS for your machine. Download BIOS if it is a newer version. (you can check yout current version when your computer boots) Go to where you downloaded the file and click, this will flash your BIOS. Make sure your battery is charged and the AC cable is pluged in.

Before you do that, try your new RAM again making sure it is seated properly. If it is not correctly installed you will not boot.

am in a similar situation: have a D600 Latitude and am attempting to upgrade from original RAM to 2 x 1GB PC2700 333 MHz sticks.  Neither stick works, have received a newer, second set of two sticks from vendor, and neither works again.  Checked installed BIOS against Dell support page and when attempting to flash Dell support website's BIOS version A16, laptop (which has BIOS version A16) notes "You are about to flash your BIOS to an older BIOS version ... "  Any suggestions?

Hi beachrat_101,

Welcome to the Community,

Latitude D600 supports minimum 128 MB and maximum 2.048 GB RAM. The Latitude D600/600M supports PC1600, PC2100 and PC2700 DDR SDRAM.

May I know the type and size of the new memory modules you bought? About the BIOS version, for your system model A16 is the latest BIOS version available on our support website. To check the BIOS version already installed on your system, access BIOS (tap F2 on start up, Dell Logo) and check BIOS version on the right top of the BIOS screen.

Thank You

2 x 1GB DDR-333 (PC2700) memory sticks

As for BIOS, upon bootup, the system notes A16 as BIOS version; it's when I tried to flash the downloaded BIOS from Dell that the laptop gives the "Warning" dialog window indicating the BIOS update would revert to an older BIOS and is not recommended

Hi beachrat_101,

The 2 x 1GB DDR-333 (PC2700) memory sticks you bought should work on your system. About the BIOS version your system has the updated BIOS version, but I am not sure why you got that warning when  you tried to flash it.

Here is a link with the BIOS version A16(File name: D600_A16.EXE): lt.dell.com/.../lt.aspx

Please check if you had tried downloading BIOS from this link above.

With the new memory module installed, try to turn on the system and check the keyboard status LED's (Num Lock, Caps Lock, Scroll Lock). If there is a memory problem preventing POST completion then Num Lock will remain off and Caps lock and Scroll Lock will stay lit)  and if system is not detecting the memory module, Num Lock and Scroll Lock will flash and Caps Lock will remain off .

Please check and let me know your findings.

That's a solid indication the new RAM is not compatible with the system.  This is an older system and newer RAM may be of higher density that it will support.

Your best bet at this point is to return the memory to the vendor and buy RAM certified to work in your system - Crucial, Kingston and others make system-certified RAM.  If Dell-certified RAM doesn't work, then you'll know you likely have a mainboard with memory sockets or a memory controller that are failing.

I've tried the new memory sticks in various configurations (single stick, double, and in combination with the original 512MB) and none of those attempts work.  Upon reboot, the CapsLock indicator flashes, by itself, about ten (10) times and the laptop turns off.

As for the BIOS, yes, that's the version I'd downloaded from the Dell Support site and when attempting to flash the downloaded version, the described "Warning" dialog window appears.

Thanks for your help, so far, any other ideas?

As ejn63 suggested it could be a problem with the new memory modules. If the system is booting fine with the old(original) memory modules installed, then the memory sockets should be fine.

Here is a link with information on Dell certified RAM for your system: lt.dell.com/.../lt.aspx

Also you may try updating the Chipset driver from this link and check if it helps: lt.dell.com/.../lt.aspx

I have the same issues with my new 1GB of PC2700 333MHz RAM modules.

My old one are working well, but this are only 512MB PC2100 266 modules.

Could it be that it's an issue of the PC2700 compared to the 2100 modules?

I know that the PC2700 are also supported, but I don't have any other idea

Thomas