I am no expert on such things but assuming the new motherboard is a good one of an identical type including the processor the computer should work.

If the motherboard is a different type it could have been thrown into confusion by the operation system which would not recognise the hardware.
A clean hard drive might make a difference.

I have had a few computers that display similar symptoms to yours and found removing the bios battery caused the machine to start. Another time replacing the battery with a fresh one did the trick.

Hope this helps. If it doesn't perhaps the replacement motherboard is faulty...