How can it be a bad hard drive when he can't get it to boot off floppy either? Is the floppy drive bad too? It's possible, but highly unlikely.
The most likely scenario is, (and it's been mentioned countless times and is well documented on this forum) is that the capacitors on the logic board have or are in the process of failing. If the capacitors are indeed in the process of failing, then they will not be able to filter the dc current running through the logic board and that is precisely the reason the hard disk will not spin up - it's not getting sufficient power.
The voltage outputs from the PSU look okay, the reason it's still not booting is because those voltages are getting lost on the logic board due to likely failing capacitors. Replacing the PSU won't make any difference, neither will replacing the hard disk.
I accept the OP doesn't want to accept this as the reason, but there is no other logical explanation as far as I can see.