Question No POST after replacing CPU - and no POST after putting back old one

[SantiClaws]

Replaced an i5 6400 with an i5 6600k on an ASUS Z170P board; didn't touch anything else. Turn machine back on, everything lights up, CPU fan spins, but no beep. Tried clearing CMOS. No dice. I thought maybe BIOS needs updating? Put old 6400 CPU back, tried again, same problem - no post. Unplugged, took out battery (brilliant design - it's under the GPU), cleared CMOS again, put battery back, plug power in, same issue. WTF?? I'm scratching my head. Any ideas?

 

[VirtualLarry]

Aww, geez. I'm sorry to hear of your troubles. The two things that come to mind, after finding out that you DID "clear CMOS", are, 1) possible bent pins in the CPU socket, and 2) possible static damage, to the CPU, or board. (It is Winter here in the Northeast, which means that humidity is lower, which means that the risk of static damage from handling is slightly higher.)

I mean, I haven't generally outright killed things from static, but it can happen, even without a visible or noticeable "spark".

Edit: Can always try the "is it truely dead, Jim"-test. Make sure a beeper is installed to the two SPKR pins on the 4-pin header, and then proceed to power-off/unplug the PC, remove ALL of the RAM, clear the CMOS (optional), and then plug in, and attempt to power-on. If CPU and mobo are WORKING, then you should hear "repeated beeps", that signal a "RAM not present error". LIke, beep-beep-beep-beep-beep, repeat. Something like that.

Also, did you remember, when you swapped CPUs, to re-connected the CPU_FAN header to the HSF fan? Some boards have a fail-safe feature, where they will not power-on, or will immediately shut down again, if they don't receive tach pulses from the CPU_FAN header's RPM_SENSE/tach wire. This is a safety feature, to prevent powering- up to full power without a HSF attached.

Edit: One more thing, if you forgot to plug in the +12V ATX12V 4-pin or 4+4-pin EPS12V (Yellow+black) connector/cables into the mobo, you can also get those symptoms, the board/fans seemingly power-up, but no POST.

 

[SantiClaws]

Also, did you remember, when you swapped CPUs, to re-connected the CPU_FAN header to the HSF fan? Some boards have a fail-safe feature, where they will not power-on, or will immediately shut down again, if they don't receive tach pulses from the CPU_FAN header's RPM_SENSE/tach wire. This is a safety feature, to prevent powering- up to full power without a HSF attached.

I did reconnect the CPU fan, and it is working, but I just noticed the case fans aren't working. I literally did not touch anything else, but maybe accidentally pulled on a wire causing a poor contact somewhere and a lack of juice to the board? I've never killed anything through static either, but I suppose there's always a first time. I was hoping maybe I overlooked something obvious which would not require me to unplug everything and start from the beginning, but that's what it looks like I'll need to do. On more than one occasion starting from scratch has helped me for no discernible reason, maybe it will work again.

Thanks for your response.

 

[DAPUNISHER]

Larry hit an important point, the pins. When you get it out of the case to test barebones, pull the cooler and CPU and check them. If it looks good, use your old CPU and once you give it power, wait 5 mins before giving up on it posting. A weird thing I run into once in a while, is that for whatever reason, plugging the monitor cable into a different port will fix black screen on boot. Sometimes it requires hot swapping the cable while the system is running. The post beep makes that a less likely issue but it never hurts to try. And as you alluded to, sometimes it feels like ju ju magic or the stars have to align just right to get things working. Spiritus ex machina and all that.

 

[SantiClaws]

Larry hit an important point, the pins. When you get it out of the case to test barebones, pull the cooler and CPU and check them. If it looks good, use your old CPU and once you give it power, wait 5 mins before giving up on it posting. A weird thing I run into once in a while, is that for whatever reason, plugging the monitor cable into a different port will fix black screen on boot. Sometimes it requires hot swapping the cable while the system is running. The post beep makes that a less likely issue but it never hurts to try. And as you alluded to, sometimes it feels like ju ju magic or the stars have to align just right to get things working. Spiritus ex machina and all that.

Thanks, I'll do as you suggest. I'm hoping it is not the pins because it seems unlikely both CPUs would have that issue, but I will take a close look. Pulling out the RAM makes it make the "RAM problem" beep, so that's encouraging. I'm keeping my fingers crossed that nothing got fried; forgetting the cost, just narrowing down what exactly went bad is such a huge PIA.

 

[DAPUNISHER]

Thanks, I'll do as you suggest. I'm hoping it is not the pins because it seems unlikely both CPUs would have that issue, but I will take a close look. Pulling out the RAM makes it make the "RAM problem" beep, so that's encouraging. I'm keeping my fingers crossed that nothing got fried; forgetting the cost, just narrowing down what exactly went bad is such a huge PIA.

Pins are in the board now, so the problem would be persistent.

 

[SantiClaws]

Pins are in the board now, so the problem would be persistent.

Ah, I did not know that. Thanks.

 

[SantiClaws]

And as you alluded to, sometimes it feels like ju ju magic or the stars have to align just right to get things working. Spiritus ex machina and all that.

Well, that was the solution. Unplugged everything, left just RAM and monitor. Posted happily first time, both with the old CPU and then the new. I... I don't know. The case fans are not working, however. I have four, and none are running. Hmmmm.