2GB ram but I have a 4GB stick installed

Is there an integrated video card that is using 2GB RAM, or does it have it's own?
If RAM is new, probably bad.  I would see about a return.

Or the machine doesn't understand 4 Gb sticks or can only handle a maximum of 2 Gb in a slot.

What is the machine's make and model?

Besides the PC/Chipset model, it can also be your OS. Windows 7 Starter for example only supports up to 2GB RAM. Does the BIOS show all RAM? There are also certain CPU's particularly Intel Atoms, that only go up to 2GB RAM.

these are good question. I need to wait til the employee is off the computer to check BIOS and also get the MOBO/CPU

it can even be a bios setting; i had this on an Asus board last week, it needed to set the northbridge ram configuration to automatic

This is a Zotac motherboard. In the BIOS I am not seeing a way to affect the RAM settings.  I found a spot in the Northbridge area For Memory Configuration, but it had stuff like Bank Interleaving (Auto), Channel interleaving  and that is set to XOR of address bits (20:16, 6), DCT unganged mode (Always), Memory Hole Remapping (Enabled), Enable Clock on all DIMMs (Disabled)...and a few other things, but couldn't see anything that would help it recognized the RAM stick is a 4GB stick.

Other info I found in BIOS:
AMi BiOS V 08.00.15, Build Date 11/18/10, ID A152PA04 and at bottom of BIOS screen V02.61 American Megatrends, Inc.

Any other ideas on how to get this mobo to recognize the 4GB RAM?

What Zotac model, with which CPU?

It is a 4GB stick DDR2 533mhz in one slot, nothing in the other slot.  BIOS shows 2GB ram.

that means that it only sees one side of the ram - and it is double sided ram, right?
probably the motherboard - or bios does not support this ram, so plse post the motherboard model, when you get access to the system

What Zotac Model and what CPU?

Thanks, I know I need to get you guys that info, I will check when the employee goes to lunch...

I was able to pull the cover just now and problem is I can't find a model number anywhere stamped or printed on the mobo. However, near the RAM slots I noticed this: DDR2-2, DDR3-1.  I wonder if that means DDR2 it requires two sticks and DDR 3 it can just use one stick?  Well, maybe not, cuz I have DDR3 stick in it now.

I may just close this question as I plan to transition this unit out of service and will probably just do it sooner, now.

DDR2 and DDR3 have their notches at different places, so you can't physically insert a DDR3 module into a DDR2 slot or vice versa. Also, if a mainboard has both DDR3 and DDR2 slots (not many have both), you have to decide on either DDR2 or DDR3 modules. You can't mix them.

If the PC uses Windows as OS, you can try the tool "HWinfo" or "CPU-Z". Both should be able to give you more detailed info on what Mainboard model is used, the chipset and version, and also the CPU model:

http://portableapps.com
http://portableapps.com/apps/utilities/hwinfo-portable
http://portableapps.com/apps/utilities/cpu-z-portable

i use  Siw for that :  http://www.gtopala.com/

The problem with Siw is that the free version (also available on the portableapps platform) is a rather old version and it will no longer run on newer OS's like Windows 8.x or 10, you'd need the paid-for version for that. The tools I mentioned on the other hand are up-to-date and will also run without problems with new OS's, and they still are free.

You guys find all the cool stuff!

Mobo is ZOTAC MCP61P
Chipset nVidia nForce 6100-405/430

Ok, I may try that, or just leave as is and replace with a new unit. Thanks for the help!