I'm guessing at this point that you have 2 - 1024 MB modules installed.
Remove one module and then see if the computer starts up with the other module. If it does, see how much RAM is listed.
Repeat the process with the other module.
I'm guessing at this point that one module is bad.
Your computer may require low-density modules, but you've installed high-density modules.
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To reduce or eliminate the risk of module incompatibilty, it's always best to install matching modules in all slots.
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