I'm not too familiar with Dell's, do they have any diagnostics on their 
website to explain lights 3 and 4?
Basic troubleshooting is to start by eliminating everything you can as a 
starting point.  If you're comfortable tinkering, unplug the power.  
take the cover off and disconnect all the hard drives, cd/dvd drives, 
floppies - disconnect power and ribbon cables to them.  You can remove 
any pci cards if present, unless you need one for the video.  Leave 1 
memory stick in place, remove the rest.   Then power up the pc.  If you 
don't get any further, my amateur guess would be a bad motherboard.  
Maybe a power surge did it in while you were out.  If it seems to boot, 
add back one component at a time, unplugging power between each step, 
and see how far it goes - if it stops again, the last part added is 
probably bad.  
Paul Hachmeyer

Gloria D wrote:

>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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