Dell GX620 - 3.6GHz Desktop 1GB RAM 80GB Windows XP SFF User Manual page 272

If the memory total is incorrect, turn off and disconnect your computer and devices from their
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electrical outlets. Open the computer cover and check the installed memory modules to ensure
that they are seated properly in their sockets. Then repeat steps 5, 6, and 7.
When the System Memory total is correct, press <Esc> to exit system setup.
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Run the
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272
Memory
Dell Diagnostics to verify that the memory modules are operating properly.