make sure you didn't leave anything rattling around...no orphan screws that might be lodged on or under the motherboard.
I'd suspect the daughter cards...
make sure they're back on the motherboard properly if you removed them.
make sure they aren't touching the edge of your processor card at some point.
make sure the insulating paper backing on the audio card is in tact or add an index card or something between it and the scsi card.
check the orientation of your 4000T scsi and floppy cables and that the floppy cable is seated both on the card and on the floppy.
make sure you haven't managed to remove/lose the little red grounding wire from the audio card...and that you reattached it when you put the machine back together.
