Could be a lot of things. I always suspect the floppy drive cable first 'cause it's real easy to not plug it in right or accidentally partially unplug it and it won't boot. I had a hell of a time getting a cdrom installed recently given the tight spaces in the 4000D. It's real easy to unplug something accidentally or switch the cable around the wrong way. I suspect this is probably your problem. Try different combinations of the power connectors, maybe there's a break in one of the old wires. Also, make sure the power supply m/b connector is not grounding to the case beneath (leads are long and can penetrate the thin plastic beneath. There could also be corrosion somewhere (e.g. my buster socket was crappy and caused either no booting or dead Zorro slots). When you power it on, if you get a faint grey screen that's a good sign that she's not dead. Think like Mr. Spock and you should be okay, don't panic.
