My PC stops working. How to check if it's motherboard or CPU?

My PC stops working suddenly. When I turn it on, the fans (on case wall and on top of CPU) spin for a second or so and then stop. It remains the same after I removed everything except power supply, motherboard and CPU. It's not power supply, because I switched to another one. I did clear CMOS but no help. I guess it must be either the motherboard or CPU. So, how can I make sure which one is faulty?

Oh, it's a desktop PC. Motherboard is ASUS LGA1151 DDR4 M.2 HDMI DVI USB3.0 H110 MicroATX Motherboard. CPU is Intel Core i5-6400 Skylake Quad 2.7GHz LGA1151 65W BX80662I56400 CPU. It was bought in Sept. 2016.