What if the computer is not compatible with memory?

My computer used to assemble a new assembly computer a few days ago with 2 512 Black Diamond, the assembly computer configuration is much better than the previous assembly computer, the new Computer 2 1G memory installed on the old computer now change back to the old computer can not use the boot a few minutes on the crash I looked for the reason is incompatible memory I'm working with 1, 512. If you want to replace the memory bar, the previous 2 512 is wasted? Why was it used before, and once again the installation could not be used? Is there any way to solve it?

1. The memory uses the alcohol cotton ball more wipes for a while. The memory slots are also scrubbed with alcohol cotton balls. Insert back the original memory bar. Before please the motherboard battery discharge. Alcoholic cotton balls, for medical use. After the power off, clear the body after static electricity in operation.

2. If necessary, graphics card, video card slots are used to wipe the alcohol sponge, wipe during the time to the motherboard battery discharge.

3. Test two of the memory is not normal, such as: First plug in 1 memory to see if it is normal, and then another memory to see if it is normal, if two are normal, the two memory to change the slot to see. 3lian Material