suspected main board problem

I’ve recently had a system shut down on me shortly before booting.It has a chaintech board with K-6 Processor at about 500 mhz. I’ve noticed that the PS was smoked(suspected lightning but not sure)replaced it with a good known used one only to smoke it too. I disconnected all cards,& unplugged all drives with no success.I purchased new bigger PS only to find out fan turns but shuts down in couple of seconds. I suspect that the board shorted but don’t trust my troubleshooting to confirm this. Can anyone suggest a method to avoid changing unnecessary parts. (it also wasted cd burner and the HD).