Hello and welcome to Bleepingcomputer.
I read your complaint and see where you are mentioning Samsung PC2-6400 memory sticks, I am assuming you have two of the same sticks by the way you described your set up.
Correct me if I am wrong.
Now you have both sticks on the motherboard at the same time, you have a no boot issue with your computer.
If you run one stick at a time in either RAM slot, you get a full boot up with no problems.
Both sticks pass the memory diagnostic tests.
I realize it sounds like an echo in here, but I like to think out loud in a thread so others can follow my chain of thought.
It appears to me that both your RAM sticks are from the same manufacture, same type and same amount of storage.
Here is a link to your computers specs.
•Amount: 2 GB
•Speed: PC2-6400 MB/sec
Memory upgrade information
•Dual channel memory architecture
•Four 240-pin DDR2 DIMM sockets
•Supported DIMM types:
◦PC2-4200 (533 MHz)
◦PC2-5300 (667 MHz)
◦PC2-6400 (800 MHz)
•Non-ECC memory only, unbuffered
•Supports 2GB DDR2 DIMMs
•Supports up to 4 GB*
◦32 bit PCs cannot address a full 4.0 GB of memory
I want to research the brand of memory you have to see if there is any issues with it working with this motherboard.
I will watch for your reply.