Suddenly no POST, EZ Debug LED CPU on

[X01X012013]

I built this PC just over 4 years ago, and it's been working until yesterday evening. This morning, it doesn't turn on anymore. All fans spin but no POST. This happened once a few days or weeks ago (can't remember exactly), but it worked again after turning it off and on. Today, however, I turned it off and on multiple times and it still doesn't work. 

 

I checked EZ Debug LEDs and the CPU one turns on as soon as I press the power button and it stays on. Fans are OK, the lights on my PS/2 keyboard flashes once but USB mouse doesn't get power. 

 

I uninstalled the heatsink to reseat the CPU and I noticed that the heatsink was never properly installed... I reseated the CPU and it still doesn't work. I also tried a few other things including unplugging peripherals and graphics card. Nothing worked. 

 

It looks like the CPU, motherboard, or the power supply became faulty. I unfortunately don't have any spare parts to test. I think most likely the CPU broke, but I also heard the CPU doesn't break that easily. My computer never shut down due to overheat, even under heavy load. Any idea where to go from here? 

 

Spec: 

CPU: Intel Core i5-6500 3.2GHz Quad-Core

Motherboard: MSI H170A PC Mate ATX LGA1151

RAM: 4x4GB Kingston HyperX DDR4

Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM

Power supply: Corsair CSM 650W 80+ Gold

Graphics card: EVGA GeForce GTX 950

OS: Windows 10

 

[Distorted_doggo]

try reseating the ram/ PSU cables/ GPU, maybe they came loose after a while. If that doesnt work you can try another power supply but as you said you dont have any spare parts to test with. Maybe ask a friend you know if they have one you can try

[Helpful Tech Witch]

10 minutes ago, X01X012013 said:

-SNIP-

Try to reseat the CPU conector on you're board. If its not plugged in correctly you will not post, and the CPU light will be on.

[X01X012013]

Unfortunately nothing worked... I'll try get some spare parts for further testing. 

[X01X012013]

Update: 

 

I tried a new power supply and it still didn't work, tried a new motherboard + CPU and it now works. So either the old motherboard broke or the old CPU broke. I don't have a way to narrow it down further but most likely the old CPU broke.