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Based on the information your provided... It look like you are running a Windows 32-bit OS, which won't see above 4GB. Can you confirm if your OS is a 32-bit or 64-bit system. If it is 32-bit, you really have no other options but to go to a 64-bit system to see all of the 8 GB of RAM.
Thank you forf anser, I have 32-bit OS