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I think that, in outline, you will need to open the device (after unplugging it and removing batteries, if any) and locate the RAM, if it is on removable modules, or the board on which the RAM is to be found, and either re-seat the RAM in its place (using full anti-static precautions!) or possibly replace the board with the RAM on it.
When RAM checks done at power-on self-test time, come up with a failure, that means either RAM is loose in its slot, or that there is a defect in the RAM memory, and/or in the board it plugs into or is soldered onto.
If you need more specifics, let me know.