Why Windows only recognizes half the RAM in my computer?

Q. Why Windows only recognizes half the RAM in my computer?
A. 1. Check if your computer or motherboard allow to increase the memory more than initial.
2. Check if your both memory sticks have the same label. It means if one stick is slightly different than initial memory, second one will never recognized. Slightly different timing between two memory is critical. Sometimes different company for the same memory has different timing.
3. Check new memory without old one.
4. Update BIOS (online) for your computer or motherboard.
5. Reset 3V battery (disconnect for one min and connect again).
Always go to the next step if previous doesn't help.
If you do something inside the computer always disconnect your power.
After changing anything restart computer.
These steps always resolve the RAM problems.