only 1 of 2 RAM units seen

Assuming you have two memory chips installed... 1. Try each chip alone in the slot nearest the processor. Do they both work? 2. Try each chip alone in the other slot. Do they both work? You only need to boot as far as BIOS to see what is happening. Skip Audares Juvo

Also, what are the capacities of each stick? Could be that the machine can only handle a set amount of RAM. "Channeling the spirit of jboy..."

It'll take 2x2Gb max non ecc unbuffered chips. No idea how it's configured right now. Skip Audares Juvo

The module may not be fully seated.

Yes I've tried all the combinations mentioned. The only other thing I can think of is "flashing BIOS" to see if second unit would be reconized, but don't know where to find correct info. thanks: Bill