p.s there was a bit of smoke coming from one of the power supply's under the machine with a nasty smell, but that has gone also. could it be some old dust that caused it?
Well this is never a good sign.. only power supply in the bottom of the machine is the transformer and it wouldnt be this. Chances are that it was a locked on coil that has now completely burnt out... youll soon find out as it will be the coil thats not firing.
I also dont like the pressing of the test button to get CPU working.. make sure you have good solid voltages from the power board, it might be that your logic voltage is taking time to stabilise, this will cause power failure to shut the CPU down.