Here is a motherboard checklist from Bryan Betts. It is old but still useful.
— Start with the power supply. Ensure that it’s working, and that it’s supplying power to the motherboard.
— Next, try a different monitor.
— Remove all expansion cards. If the machine boots, replace the cards one by one until it doesn’t.
— Check motherboard for signs of blow components.
— Try swapping the CPU with a known-good one.
— If the video controller is built in, disable it and try another video card.— Buy or borrow a POST card. There should be a usb type on amazon.com.
— Check the CPU fan.
— Check the RAM chips by replacing them with known-good ones.
— Disable external cache.
— Remember to keep a record of everything you do.
— Take anti-static precautions.