Computer All Of A Sudden Won’t Boot - Red CPU Debug Light ON

Greetings All. A few days ago, my PC all of a sudden booted with no display, which was a first, but it booted normally again 10 minutes later. Then the next day the same thing happened, I realised the CPU Debug red light was on this time and searched for a solution to no avail. I have tried restarting CMOS, both battery and jump start, which did fix it temporarily, but the next time I booted the PC the debug light appeared again. I also took out the GPU, and checked the CPU for bent pins. I have tried testing the ram sticks also and the red light did not budge.


Also, I tried switching the ram sticks to first and third slot instead of 2nd and 4th ( where they would normally be ) just for the red light to disappear, allowing my PC to load up. I ended up using it like before, running games and all, just for the CPU debug light to appear again the next time I tried to boot it up. This started happening a few days ago also which is a bit weird. I will list my specs below in case it helps.

Ryzen 5 3600
GTX 1650 Super
B450M Mortar Max
HyperX 16GB Ram
600w PSU

( I have had this PC for just over 2 Years and bought all parts from the store )

My PC hasn’t had any issues before and I haven’t done anything to it either so i’m not too sure what my problem is here. I have no clue what it is, sometimes it would boot just fine, just for the red light to appear the next time I load up. Maybe a faulty Motherboard or CPU, or even the ram sticks? I just need a few heads up before I start spending money and replacing parts.

Any sort of help would be appreciated Thanks.

Sounds pretty intermittent.

its hard to know what your computer is doing without seeing it first hand, here is how i would go about it seeing as you have tried some other troubleshooting but have been getting some pretty intermittent results.

- Reset the cmoss but this time make sure the power cable is unplugged from the computer, take the battery out and then hold the power button down for 30 seconds.

- Plug the battery back in and the power cable.

Try to flash the bios using the flash bios button on the back of your motherboard. The usb port closest to the flash button will be the port to use.

If you can get the PC to function as intended set to factory defaults in your bios and then try to get to windows. if you can make it to the log in screen then restart the computer do this several times to see if the PC can make it back to that state. Make sure you change up the situation like actually shutdown the PC a few times instead of restarting, and then power back on.

if you can cycle the PC 5 times at least then you know its got a good chance.

Hey, Thanks for the reply

Today I started by removing the battery and holding down the power button for 30 seconds, which did manage to work after a bit of a light show from both the boot and cpu debug led lights.

I then set the bios to default and hit save and exit, as my PC rebooted the issue started up again, and the CPU light was on.

After a failed attempt with the bios flashback, I tried the ram sticks once more to no avail.

Do you think that maybe it could be a motherboard issue? everyone that has ran into a similar problem had a faulty mobo.

its hard to say with limited situation because CPU light can happen from benign things as well. Overclocking can cause a CPU light and if this is the case and you were OCing then the CPU may not be broken.

Last ditch effort take the motherboard out of its case and try to troubleshoot it because it could be having grounding issues. Put the motherboard on something like a desk where its not going to earth to any metal and then test from there.

Because the PC is in a intermittent state this is a good sign because if the CPU was dead then you would not get the PC to boot some of the time like it is, it would just never do anything with blank screen every time.

If the PC is shorting where it shouldn't like on the case then it can cause the computer to malfunction and cause intermittent issues like booting only sometimes and not others. I only say this because i don't really know without trying to test myself so am limited in what advise to give.

These are just step i would take if i was working on an unknown computer to me in person that had this issue. If a part burns up then usually it will go straight away not over time.

So just a quick update :

I had a test with all the ideas mentioned above and it seems that every time I either reset CMOS, take my ram out and place it back in, or do the same with the GPU it boots up normally with a few of the debug lights flashing on and off, allowing me to use the PC with no issues.

Then, like it always does, it goes back to not booting with the red CPU light the next time I boot up. I’m just not sure what to do as it does boot and work perfectly fine sometimes, but upon restarting, fails to load along with the CPU light back on.

I’m gonna try and play with the bios if I manage to load up again and if that doesn’t work I will probably take it in for a checkup as I have no clue what it could be.

browncat2 said:

Ryzen 5 3600
GTX 1650 Super
B450M Mortar Max
HyperX 16GB Ram
600w PSU

what kind or brand of "600w PSU" do you have in your computer, browncat2?
maybe try installing & using another 600w PSU (or higher one like 700w) from another manufacturer to see if you get the same result.

also try using another Ryzen 5 3xxx CPU as well

if all else fails or no improvement after doing all these things, it could mean motherboard replacement time

Have you tried the---load optimized defaults ---in the bios?
The light should be on whilst a bios update is in progress,check your bios version with MSI.
Could you check if the operation of the light has any other purpose,there should be something in the User Manual.

I have tried all I could at this point, from loading defaults, to bios flash ( blinks 3 red lights before stopping, tried numerous times to no avail ). And it won’t even let me update bios as loading into M Flash needs the PC to reset which ends up turning it off, not letting it load up again due to red CPU light appearing once more.

It literally loads up sometimes and allows me to use it like I could before, then after restarting goes back to red CPU debug light. At first I thought it was the motherboard over all the other parts, now i’m second guessing for the PSU ( 600w Bronze EVGA ) as CPU may not be getting enough power to boot ? no clue at this point, also do not have spare parts to test PC so that’s out of the picture.

Aside from that I have tried pretty much everything listed above plus more, I will write it down below in case anyone views this and types a suggestion I have tried.

reset CMOS ( battery & jump start )
flash BIOS ( only 3 lights flashed )
reset CPU
reapplied thermal paste
replaced CMOS battery
tested ram sticks
reset GPU
set bios to default
double checked all cables and parts are not loose

Thank you to everyone who wrote a suggestion.