I have an A4000T as well, I gave Amiga hardware database a copy of the manual which you should follow.
http://www.bigbookofamigahardware.com/bboah/media/manuals/A4000T.pdfwhat do you have installed in the system Hardware wise?
I've had this problem before but cannot clearly remember if it was the IDE/SCSI card is not firmly inserted. Re-seat the Processor card as the A4000T is temperamental if this is not firmly installed. Clean the connectors with a cotton bud and cleaning fluid.
Check your jumpers also on the motherboard see section C3 in manual. there jumpers for the processor card. (page44)
Unplug all your hardware but leave the sound & scsi/ide installed and memory and also the floppy drive.
Make sure you are firmly grounded and power is unplugged as that case will fry your board.
Let me know how you get on.