Hi Shoom,
Welcome to the forum! Did you have video when you initially powered it up? In other words...did you see the usual BIOS information and the various screens as the CPU boots up. Or was there no video at all, and all you got was the "Error 43"?
As a starting point, I'd check cables and connections, watch out for the power connections to the motherboard, it is possible to reverse these two plugs. This will result in immediate damage to the motherboard if powered on with these plugs reversed. This
picture from the database shows the power plugs at the top left. The picture is of the newer motherboard as none of the pics of the old one show the power plugs clearly.
Pull the BIOS battery out for an hour or so, I had a D8B that appeared to be completely dead (no video, no disk activity...just fans), that was cured by leaving the battery out for a couple of hours and then resetting the BIOS settings. I can only assume that the battery was failing and the BIOS settings had got so corrupted that it wouldn't do anything at all.
BIOS settings for the mother boards are
here for the new, and
here for the old motherboards.
Not on a D8B, but I have had computers fail to boot with a faulty mouse or keyboard. Can you test your mouse and keyboard on another computer? If not just unplug them and see if it boots. It should boot without them, but if not you should see something on the screen complaining about the lack of a mouse or keyboard.
Regards
John