If it`s the floppy light, check the cable.
I rebuilt my 4000 with the floppy cable plugged in the wrong way around and the light stayed on and stopped booting.
If it`s the HD light, unplug the HD and make sure the floppy drive is empty and boot up. If it gets to the "Insert Disk" screen, then then either the IDE cable is in wrong or loose, the HD could be toast, or the onboard IDE port is fried.
