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I have a Dell XPS 400, 3 GB of RAM (1GB x2 and 512MB x2). I powered it on this morning and got the 3 and 4 diag lights; monitor shows no input. Dell docs say that "memory modules are detected, but a memory failure has occurred". As suggested, I went through the process of removing the modules one by one, even purchased new modules, but the lights are still there. Any clue what it might be? Thanks!

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Could be a busted motherboard...or CPU, as sometimes the CPUs have memory controllers.

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It sounds like a problem with either the processor, memory controller, PCB traces to the memory banks, or the banks themselves. – TuxRug Jul 30 '10 at 23:20
Wow, this place is about as awesome as Any way I can run some sort of diagnostic myself - Dell wants $50 for it? Or would it make more sense to just go out and purchase a new motherboard? – alex Jul 30 '10 at 23:40

Check the motherboard for swollen/bulging capacitors.

If they show signs, the motherboard needs replaced, or have someone skilled in soldering to replace the bad caps.

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