Hahha, accidentaly i also got a 2408, and i didn't properly screw it in, but that's another story. And yes, i'm on pc.
The light on the back, which confirms that the computer is getting juice (and should always be green when there's a powercord inserted), is dark. It gets green when you unplug and plug in the cord again, but as soon as you boot it, it goes dark and nothing happens.
The weird thing for me is that everything DID work perfect, then i got the "bad harddrive", and now it doesn't even start.
I did only change one thing in the bios, that was changing the grafic card from "onboard" to pci. Well, it was always PCI, and i DID use the same slot for the old and the new card... But there's no real way to fix this since it's not even accepting power.
What more info do you need? I really apprichiate this

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I'm going to try to reseat and screw all the cards back, but is this really it?