I have a Dell, XPS 400 with 3 gig ram. I'm not sure what the processor is, I just know it's a duel core intel. I have upgraded windows xp to windows vista home premium.  I left for the store yesterday and when I got home the computer had shut down. I turned it on and it wouldn't boot up but could hear the fans running. The number 3 and 4 diagnostic lights are burning. Number 1 and 2 are off. Dell said it could be bad ram or the motherboard. It's out of warranty so am trying to fix it myself. I don't want to believe it's the ram because it's fairly new. I have removed the ram and tried different slots and sequences but that changed nothing. Still the 3rd and 4th lights burn. I get no beep code or anything like that. There is a green light on the motherboard that burns when the power cord is plugged in. I don't think it's the motherboard. At least I sure hope it isn't. Any help would be greatly appreciated. If more information is needed let me know.
Thanks!
Gloria

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