Unplug the PSU from everything. Then plug the PSU in and turn it on. If the Power Supply's fan starts it could be two things. The motherboard might be faulty, or the PSU has too much dirt accumulated in it.
The next steps are harder. Disconnect every board or peripheral that plugs into the motherboard. Test to see if the ROM boots. If it will, start connecting the components one by one. I start with the hard drive first. You only need the hard drive to boot as far as a DOS boot.(Submarine?)
Now reconnect each component until the error occurs.
You may also have a bad RAM stick. These usually are plugged into the motherboard in pairs. Remove the two higher RAM sticks and try again to boot. You can mix and match the sticks until you isolate the bad one.
I hope this help. Commodore/Amiga tech is back in business
! (I was a certified Commodore repair tech back in the day)