Kongtiao, thank you for posting to the Microsoft forums.
What is the exact diagnostic tool you refer to?
How much memory does Windows Vista report?
Check this one of three ways
Click "Start"
Right-click on "Computer"
Click "Properties"
Your memory will be displayed within this Window to the right of "Memory (RAM):"
or
Click "Start"
Type "msinfo32" (without quotes)
Your memory will be displayed to the right of where it says "Installed Physical Memory (RAM)"
or
Click "Start"
Type "dxdiag" (without quotes)
Your memory will be displayed to the right of where it says "Memory:"
Any issues with your memory will be reflected within these utilities. If you are using a 3rd party application to check the quantity of memory then you may need to check with the manufacturer of that application for future support.
If you require further assistance then please reply back to this thread.
regards,
Aaron Barth