PC not POSTing

Not open for further replies.
Hi there, I have been reading forums for days now and trying all the various suggestions I have found, but still have no joy in fixing this unusual problem. If anyone could offer any advice at all I would be incredibly grateful!

I run the following setup:

Asus P5K3 Deluxe Motherboard
650W Dark Power Pro "Be Quiet" PSU
Intel Q6600 Processor
Gainward 9600GT Graphics Card (1Gig)
2GB Corsair TwinX DDR3 RAM
750Gig Samsung HD
Phillips DVD-RW (not sure of model number, now disconnected from PSU and mobo)
HP 2408 24" Monitor using HDMI cable

I switched on the PC one night last week and got a black screen. No POST, no BIOS, nothing. Admittedly a week before I had tried to switch it on and it didn’t boot, but I just turned it off and back on and it went fine.

The green motherboard LED comes on solid so there is power, all fans spin up including the CPU fan, the hard disk spins up, and then it just seems to "stall", and does not even POST never mind go into BIOS or start to boot. I know that it definitely is not just booting up and not outputting to the screen, as the graphics card fan stays at full speed, normally during boot once the driver is loaded it slows down to dynamically maintain temperature whilst reducing noise. If it was simply not outputting to the screen then this fan would slow during boot, even though I can't see the output.

It was built in May and has worked absolutely fine until last week. I have not added any new hardware, loaded drivers, flashed BIOS etc. since May. I have gone through the following steps to try and resolve it:

1) Borrowed a known working monitor, then graphics card, fault remained
2) Bought new identical RAM, fault remained (I was going to upgrade to 4 Gig anyway!). Also tried all combinations of single/paired modules
3) Bought new identical motherboard, intending to return the old one if that was the fault, put my CPU, PSU, graphics card and RAM in the new motherboard on a test bench and the fault remained
4) Put my CPU in another known working socket 775 PC – it ran absolutely fine
5) Also put my graphics card in the same known working PC, again it worked fine
6) Replaced CMOS battery – no help

All of the above leads me to believe the PSU is faulty, as the fault did not occur when I used my CPU and graphics in the known working machine. My next test is to borrow a PSU so I can rule out a fault on the EATX+12V rail that supplies the 8pin connector on the P5K3 board.

However one thing confuses me a great deal; I can get the PC to boot, probably half the time, by clearing the CMOS i.e. switch off at mains, remove CMOS battery, and bridge the appropriate jumper. This works about half the time as I say, though this may be due to me not giving it enough time to clear properly (I am getting frustrated now and hence impatient!). For example, last night I got home from work, set the CMOS to clear, made dinner, then put the jumper back to normal and it booted fine, then I just pressed F2 to load setup defaults and I enjoyed 5 hours of trouble free computing. Sure enough when I turned it off when I was going to bed, I tried to reboot and it would not POST. I fail to see how a PSU problem would cause this behaviour, which makes me think it is either a motherboard fault, or a fault with the BIOS chip or CMOS battery. But surely the odds of me getting identical failures on 2 consecutive boards is basically impossible? And I replaced the battery and have checked voltage on the original and replacement and they are both showing 3V.

The easy solution would of course be to leave it running constantly, but it is right next to my bed and the noise from the CPU fan with dynamic fan speed control (which is the BIOS default) is unbearable!

If anyone has any ideas I would love to hear them, otherwise I will post the results of my PSU trials if/when I can borrow one!
Have a look here: Tutorial: No POST (Power On System Test)

Thanks for the link - I have tried all of that apart from booting without the battery. My PC is immaculate inside, and the bench test of both the "old" and identical replacement motherboard proved fruitless. I believe it's some sort of issue either with the EATX+12V supply from the PSU (which is on it's own rail) or perhaps some sort of BIOS corruption that is occuring when I reboot that is causing the board to ask for too much power from the PSU. The only thing that I doubt about the latter is that I tried a brand new board and found the same problem. Unless of course my PSU has somehow damaged both the "old" and replacement boards when I connected it up.

Anyway, as I say thanks for the link, that page had not come up in my searches and it's one more thing I can try.


Posts: 13,806   +3
Thank-you for the feedback and further information on your issue

If all things have been successfully completed in the "No Post" tutorial, then sadly the only are option is faulty hardware. ie Power Supply; Motherboard; CPU; Ram

It would be ideal as a first measure to replace with a known working Power Supply (as per the tutorial)

It is a matter of swapping parts, or returning parts under warranty (if warranty exists)

Good luck and keep us posted :)


Posts: 10,610   +464
I think it may be the PSU based on what you said.

Clearing the CMOS may just be coinciding with some odd issue with the PSU. I had a PSU once that would only boot the comp if it was unplugged, power switch toggled while it was unplugged, then plugged back in and tried.
Changed the PSU out for the loan one on my trusty bench and it is working fine. Built it all back up in the case with the loan PSU and rebooted many times without issue. The failed PSU is now winging it's way back to Scan for refund/replacement.

Thanks all for your input!!!
Of all the many forums I visit, this is the best.

By that I mean you have:

1) A list of known resources STICKIED
2) A good user group who wants to help

For those reasons I can't say thanks enough.

I probably would have got there in the end, but by coming here I got there sooner, and more to the point knew the reason I came to my result. And I am a bit of a geek so knowing why is pretty much as important as the result!


Posts: 13,806   +3
Now that's good feedback :grinthumb

I might even save your post to quote to others at times ;)

It's nice to give thanks, and warmly welcomed
Come back anytime, for any issue you may have, if I see your name I'll reply immediately.

Thanks again :)
Not open for further replies.