VIntage IBM PC/XT 5160 (not working) in CANNING VALE, Western Australia for sale

This is an original IBM PC XT, model 5160. It was working recently, but failed after about an hour of running (see below for failure details).
It comes with an original 5151 green monitor and buckling spring keyboard. It has one 5 1/4" floppy drive and a 10MB hard disk. It also has an original IBM async adapter card in slot zero.
Cosmetically, it's in great condition (considering its age) and would make a fantastic retrocomputing display piece - but one I don't have room for anymore. It could presumably be harvested for parts, but please don't tell me if that's your intention :)
Failure details for the technically minded:
It powered off while showing it off (my kids were impressed up until that point). Initial suspect was the power supply so I replaced the 30-year old capacitors.It now powers up and the voltages are within spec, but it doesn't want to boot (not even a beep). Some probing with an oscilloscope shows clock and activity on the address lines, but that's as far as time and my skillset will take me.
The next troubleshooting step would probably be to investigate the "checkpoints" (the PC/XT equivalent of POST, but I'm handing that responsibility on to you!