Question Installed a new CPU and now my PC boots for one second and shuts down

Oct 3, 2021
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I got a new CPU, an Intel i9-9900KF, to replace my old cpu, an i5 (cannot remember the exact make), and when I finished the installation my pc shuts down after around one second each time I turn the power on.

In addition to this I reinstalled my old CPU hoping I could continue using my pc to find out what was wrong and now it doesn't work in a completely different way using that one. It boots for maybe 10-15 seconds with no image showing on my monitor and then shuts itself off before starting and trying again with the same outcome.

We also tried running just through the motherboard with no CPU and the pc starts for a few seconds, shuts down, then boots properly with no image showing on the monitor again. It does not shut down this time though.

I have looked at many supposed "fixes" like changing the number of sticks of ram and their placement, removing my GPU, removing the motherboard battery and putting it back after 5 minutes, checking all cables from the power supply are connected. Nothing seems to help with the problem.

A friend came to look and couldn't figure it out and said that since power is getting to all individual components and they seem to be functioning (lights coming on, fans whirring, etc) that it doesn't seem like there even should be a problem.

I need this pc quite desperately for my work so any assistance would be greatly appreciated.
 
Oct 3, 2021
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Not much anyone can do without knowing the exact i5 you had and the motherboard you now have.

In fact, all of your specs are needed in order to properly try and troubleshoot.
The old cpu is an i5-6500
The motherboard is a Gigabyte GA-B150-HD3P
16GB RAM
Nvidia GTX 1660 ti GPU
I also have a 125GB SAD

Would there be any other information needed?
 

DSzymborski

Titan
Moderator
The old cpu is an i5-6500
The motherboard is a Gigabyte GA-B150-HD3P
16GB RAM
Nvidia GTX 1660 ti GPU
I also have a 125GB SAD

Would there be any other information needed?
The motherboard is completely incompatible with the new CPU. 100-series motherboards for Skylake and 200-series motherboard for Kaby Lake absolutely cannot run Coffee Lake CPUs. 300-series motherboards for Coffee Lake and Coffee Lake Refresh CPUs absolutely cannot run Skylake or Kaby Lake CPUs. The motherboard are not electrically compatible. And even if you were able to run this on a technical level, a budget motherboard is an exceedingly poor match with the 9900KF.

Why your old CPU doesn't work is harder to figure out. First thing I would check to see if you bent any pins on the motherboard.
 
Oct 3, 2021
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The motherboard is completely incompatible with the new CPU. 100-series motherboards for Skylake and 200-series motherboard for Kaby Lake absolutely cannot run Coffee Lake CPUs. 300-series motherboards for Coffee Lake and Coffee Lake Refresh CPUs absolutely cannot run Skylake or Kaby Lake CPUs. The motherboard are not electrically compatible. And even if you were able to run this on a technical level, a budget motherboard is an exceedingly poor match with the 9900KF.

Why your old CPU doesn't work is harder to figure out. First thing I would check to see if you bent any pins on the motherboard.
What would you recommend as a good replacement motherboard that would be compatible with the information I've given?

Going to take it into a shop and see what they can do but I'm going through with the upgrade if I can.
 

DSzymborski

Titan
Moderator
Something like a Gigabyte Z390 Aorus Pro or an ASUS Prime Z390 would be suitable. If you want to do this particular upgrade, you need one of the better quality motherboards and an effective cooling solution.

There's also the issue of PSU you're using. If you're on an older or junky PSU, it wouldn't make sense to invest in an expensive upgrade without remedying a power delivery situation.

Lastly, are you still able to return the 9900KF? Intel's not known for dropping prices on their older parts still being sold, so there's very little reason to go with a platform that's already had two generations after it and about to have a third. The 9900KF and the good motherboards for it basically sell for as much as the equivalent parts of the current generation.
 
Oct 3, 2021
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Something like a Gigabyte Z390 Aorus Pro or an ASUS Prime Z390 would be suitable. If you want to do this particular upgrade, you need one of the better quality motherboards and an effective cooling solution.

There's also the issue of PSU you're using. If you're on an older or junky PSU, it wouldn't make sense to invest in an expensive upgrade without remedying a power delivery situation.

Lastly, are you still able to return the 9900KF? Intel's not known for dropping prices on their older parts still being sold, so there's very little reason to go with a platform that's already had two generations after it and about to have a third. The 9900KF and the good motherboards for it basically sell for as much as the equivalent parts of the current generation.
As you can probably tell I'm not the most well versed in these areas so I'm a little confused on some of the areas you spoke of. I only went with the i9 since I thought it would be compatible but since it's not it's as good a time as any to rethink things.

I'll take what you've said and relay what I can when I can get somebody to take a look at it and see what would be the best approach for me going forward. I'm not looking for something super high end, I was just hoping to future proof a little so I didn't feel the need to upgrade every few years for fear of falling behind and not being able to do the things I want.

I have a 750 PSU right now which I think and would hope is good enough for what I'm wanting. I also think I should be able to return the CPU but I'll do more research into that after I've decided whether it would be best for me to keep it or not.

Are the boards you suggested compatible with DDR4 RAM or would I also have to replace those if I made the switch?
 

dracobeats

Commendable
Dec 31, 2018
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Have you tried clearing the cmos by removing the cmos battery or jumping the pins. This may get your old cpu to work but I’m not sure.
 
Oct 3, 2021
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Have you tried clearing the cmos by removing the cmos battery or jumping the pins. This may get your old cpu to work but I’m not sure.
I have tried these methods yes. Sadly to no avail.
I'm all but convinced at this point that I accidently bent some pins when installing my new CPU. I'd rather not risk making a worse mess of things and let someone with experience give it a look.
 

dracobeats

Commendable
Dec 31, 2018
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1,510
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I have tried these methods yes. Sadly to no avail.
I'm all but convinced at this point that I accidently bent some pins when installing my new CPU. I'd rather not risk making a worse mess of things and let someone with experience give it a look.
Yes that definitely could be the case.
 

DSzymborski

Titan
Moderator
As you can probably tell I'm not the most well versed in these areas so I'm a little confused on some of the areas you spoke of. I only went with the i9 since I thought it would be compatible but since it's not it's as good a time as any to rethink things.

I'll take what you've said and relay what I can when I can get somebody to take a look at it and see what would be the best approach for me going forward. I'm not looking for something super high end, I was just hoping to future proof a little so I didn't feel the need to upgrade every few years for fear of falling behind and not being able to do the things I want.

I have a 750 PSU right now which I think and would hope is good enough for what I'm wanting. I also think I should be able to return the CPU but I'll do more research into that after I've decided whether it would be best for me to keep it or not.

Are the boards you suggested compatible with DDR4 RAM or would I also have to replace those if I made the switch?
What 750W PSU? There are excellent ones and terrible ones.

DDR4 is the standard until the next generation that is not out yet.

One thing to remember in future upgrades of this type is to always check your motherboard's page on the company's website. There's always a detailed list of compatible CPUs. Same socket doesn't necessarily mean compatibility; sometimes later CPUs require a BIOS update, sometimes CPUs are too high wattage for a budget motherboard and not listed, and sometimes, CPUs simply are not compatible with older boards of a socket. Your Skylake motherboard, for example, would have needed a BIOS update to work with Kaby Lake motherboards, with Coffee Lake CPUs incompatible for a consumer (there are proof-of-concept hacks that have been done, but nothing for practical use).
 

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