My son has my family’s oldest gaming PC, it’s an i7 4790 with a 1660 TI and 16GB DDR3. It wasn’t booting the last couple of days. I had time to look at it so we disconnected everything and threw it on the table with some good light and connected it to power so I could see what it was doing.
It was clear his three case fans were all dying, one was completely dead. One was in poor condition and one was starting to make noise. I already had extra case fans brand new in box sitting in my house, but I assumed old fans weren’t what was keeping it from booting.
We removed all three bad fans, and with the case wide open, both sides front and top removed, I blew it out a little bit with canned air. It wasn’t that dirty, just a little bit of dust came out. I checked with my fingers to see that the ram seemed seated and that all the connections seemed okay, but I didn’t disconnect and reconnect anything, I just touched it.
I turned on the PC with no case fans (only an old CPU cooler connected) and it booted up. So we installed the three new case fans, and tested it again. It booted up again. We put it all back together and connected all the peripherals and it’s working absolutely flawlessly.
So I am asking a question, but I want you for context to know that I have repaired hundreds of PCs, maybe close to a thousand. I have never fixed a boot issue by replacing case fans. I have read that some 20+ year-old PCs maybe would have that issue, but from what I understand a 12-year-old PC should not have boot impacted by case fans. So here’s my question: was this just a ghost in the system, or is this actually possibly a real thing?
TL:DR We fixed his computer with three new case fans and the tiniest bit of canned air. Help me make it make sense.
I’ve built a lot of computers in my lifetime and my only guess when reading your post was that somehow one of them was causing a short and that short was somehow preventing the system from successfully posting, but I’m not sure how that would work exactly.
My level of technical knowledge ends about there. I can troubleshoot and swap hardware all day, but idk how a case fan would cause a system not to boot specifically.
Unless… Was one of the case fans running from the CPU header for some reason? Maybe the board thought the CPU fan was cooked and it was preventing a boot for safety? I’ve never seen anything like that safety speaking, but I could believe it exists.
Maybe the board thought the CPU fan was cooked and it was preventing a boot for safety? I’ve never seen anything like that safety speaking, but I could believe it exists.
I’ve owned and worked on computers that have that as a safety feature. If the CPU fan wasn’t connected or wasn’t working, they wouldn’t boot. They would usually have a beep code to let you know, but that’s assuming that there’s a motherboard speaker and it’s working.
A shorted fan would probably trigger it, as they would usually use the third cable on the fan connector to measure the rpm and check that the fan was spinning 👍
This would be my guess as well. A short or a seized fan causing draw to spike in a way the board didn’t like. OP doesn’t give any detail on what “wasn’t booting” means. If it’s failing to post it should still throw you a code in some manner as a starting point.
Man I used to check if systems would post without a cpu cooler installed at all back in the day. I wouldn’t run it for more than a few seconds but just long enough to make sure it was posting.
Had a buddy burn his finger pretty good because he wanted to know how hot a cpu would get without a cooler lol. Turns out they get hot enough to burn humans within a couple seconds lol
Pretty easy to guess that! 100°C is boiling, and a 50°C idle is ≈120F (about the same temp as the hot water from a household tap), so holding onto a CPU doing more than idle is going to be between 120F and boiling.
But to your point, I actually have my BIOS set to not boot if the CPU fans die. Some BIOS might have additional settings for each fan header, so a dead case fan could certainly cause the computer to fail POST.
Thanks for the response. I’m not trained in PC repair nor is it my job but I’m pretty good at it which is why I’ve done tons of free PC work for non-profits and a little bit of side jobs fixing or building PCs for people I know.
I actually don’t know where they were plugged in,but my son does. I was trying to teach him a bit so as I removed the screws from the fans at the front and pulled on each cable so he knew which one to unplug, he actually disconnected the old and then later reconnected the new fans, not me. I made sure he paid close attention to the pin locations, so he can probably tell me when I get home. In theory though, modern PCs should be able to boot with no CPU cooler, they’ll shut down quickly when they get hot though. I’ll look into this.
Yeah I mentioned that in my other comment. I always test boot my new builds while outside the case with just the CPU installed. I like to make sure it’s posting each time I add new hardware so I can know before I put it all in the case that something is wrong. I have never had a board refuse to post without a cooler or fans connected, but they will give warnings out the wazoo though.
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How old is that power supply? I’ve seen several that just the act of it being unplugged for 5 minutes allows it to boot again.
The theory being a capacitor or such needed a chance to calm down a bit somewhere, and something in the power supply or mainboard would proceed until power was back to normal.
Especially common if there’s brownouts or surges.
I have an extra PSU sitting around and planned to install it. The current one is about 6 years old. I also thought this, but I figured I would see if it continued to work well. So far he’s had 2 days with only replacing the case fans and it’s working great. If it goes out again, the first thing I’ll do is swap out the PSU. Like I said, I was expecting to, even planning to. But it worked without it. So maybe it won’t work for long. We’ll see!
Computers are smart, if a cooling device doesn’t want to cool. Then it shall not get hot at all
