PC won't boot -no power but green m/board light on

  captainhaddock 19:44 12 Apr 2008

I've just got a new PC to replace my 2003 Carrera PC so I thought the old PC can now go in my son's room. As it's been operating perfectly ok, but in a dusty corner of the lounge, I decided to vacuum all the clogged up air vents (it was unplugged at the time) which I have done on several occasions in the past. I then took it upstairs - removed his ancient PC and set up his 'new' replacement. On pressing the power button it seemed that absolutely nothing happened. Disconnected & reconnected everything with the same result. Opened up the machine to see if there were any obvious loose connections to no avail.

The PC is a Carrera Octan Ultimate 2600+ running XP. The motherboard is an Asus A7V8X-X with one stick of 512MB memory, an AMD Athlon 2800 XP CPU and a 128MB GeForce 4 Ti4800SE graphics card.

I did notice that the green light on the motherboard was on (not flashing but on) and when I pressed the power button on the front of the machine the two chassis fans, the CPU fan and the PSU fan would all flick - if I continuously pressed the power button on the front of the machine (on & off like an old decathlon video game) then I could get most of the fans to rotate slowly but continuously but the hard drive nor anything else would appear to stir. There is a one second surge of power to the fans if I press the off button on the back of the machine whilst flicking the power switch on the front.

Disconnected all PSU connections inside and reconnected, then the same with all drive cables, taken memory out and put back in still to no avail. Took out the PSU and put in the one from his very old PC with the same result.

I have tried shorting the power switch and the CMOS. I have taken out all the PCI cards and tried booting up, I've taken out all the cards including the graphics card, re-installed them but still get exactly the same result.

I have taken out the CPU heatsink, put in some new thermal compound as it was cracked in places. I've blown out all the dust and still exactly the same thing happens.

My son keeps telling me he's all right having his old PC back but he's been moaning for ages about Windows Millenium because he can't use iTunes with it nor run half his games and loads of other stuff runs really slowly as it only has a 40GB hard drive and 256MB of memory.

I am hoping that nothing has blown, like the motherboard, whilst vacuuming it or whilst going on the long journey upstairs! The only saving grace is that I'd just backed up all the files I wanted to keep.

If anyone has any ideas or suggestions they will all be greatfully accepted.

Many thanks.

  johnnyrocker 19:46 12 Apr 2008

sounds like for some reason your psu has died?


  captainhaddock 19:53 12 Apr 2008

Thanks Johnny - it might be, but I did try the PSU from my son's old PC and got the same results. However the old PSU didn't have a connection for the Soundblaster drive but I don't think that would make a difference when booting up. There is some power getting through as the green light comes on and the fans twitch - I'm not sure if that could still happen if the PSU had gone as I'm not a technician. Thanks again.

  Fruit Bat /\0/\ 20:55 12 Apr 2008

If fans won't run then either switch, PSU dead, mobo, or cpu.

"I have tried shorting the power switch"

remove connections from switch at motherboard and short the two connections on the board very quickly, a prolonged short just signl the bord to power off again.

As you have remade all connections (4 pin next to cpu fitted?)

refitted cpu , changed PSU, could be a bad borad.

just make sure there is no short between board and case

remove board lay on paper connect cpu + fan, psu, video card + monitor and memory only and switch on by above method.

  captainhaddock 00:36 13 Apr 2008

Hi Fruit Bat,

Thanks for your help. I'm glad you clarified shorting the power switch as I had been doing it for longer but unfortunately it has made no difference - but at least I know how long to do it now.

I'm not sure about the 4 pin next to the CPU as I can't see any other connections near it apart from the 3 pin power socket for the CPU fan - any further info on this or is it only on a few mobos? (The PSU has a 20-pin ATX connector which has been powering the board for five years).

I've done as you suggested, but with the same result. However, it is interesting to note that if I hold the power short then the fans (all 4 - the CPU fan, the two graphics card fans and the PSU fan) all twitch on & off, without ever really turning, for a good 8-10 seconds, sometimes longer. Nothing seems to wake the monitor from sleep though so probably don't need to connect this yet.

Would this suggest that the mobo has gone (or the CPU or RAM) or might it still be something else?

Shouldn't the PSU fan come on straight away or does that need a return instruction from the mobo to fire up?

Thanks very much for your help again.

  Incony 03:23 13 Apr 2008

does the video card fire up.. or does the screen say no signal?

if the mobo green light is on... the mobo has power.. but for some reason the boot sequence isnt starting.. if so the video card wont fire up either and the screen will say no signal.. so you get nothing happen.. no clicks or noises from the hard drive.. no video... nothing..

the cause of that could be a corrupt cmos... have you tried resetting that yet..? its done by removing the mobo battery.. but... if you do it.. read the mobo manual first.. one needs to discharge the capacitor that holds the cmos power stable, and the instructions on how to reset the cmos will be in the mobo manual..

  Incony 03:37 13 Apr 2008

click here

the manual.

Motherboard diagram is on page 1-7 (Chapter 1, Page 7). Note the "CLRTC" jumpers next to the CMOS battery. (The battery looks similar to a U.S./Canadian nickel.)

Page 1-14 shows instructions about how to reset the CMOS (Clear RTC RAM).

  Incony 03:59 13 Apr 2008

page 24 shows the cmos battery and how to reset the cmos

  captainhaddock 20:00 13 Apr 2008

Hi Incony,

Thanks for going to all the trouble of looking the info up. I had tried it before but I've given it another go and still the same thing is happening. Presumably starting up wouldn't make any difference if the button cell battery was dead? Not sure whether it is or not but it has never been replaced in five years.

I can't see any obvious signs of leakage or burn out on the mobo but I think it's looking more and more like something's 'blown'. I could probably buy all the components cheaply on ebay but would have no guarantee of them working or not doing further damage - it would be good to be able to narrow it down to what has actually gone though so I could just buy one board!

Thanks again for your help.

  daxian 22:46 13 Apr 2008

hi captain haddock...
i would advise getting a new psu ,as this is more than likely the culprit ...i know you have tried another from the older machine ,but it is possible that it is not strong enough for the board .
i have had similar experience of the symptoms you describe..and all turned out to be the psu .Dave.

  woodchip 22:51 13 Apr 2008

You do need a PSU with enough watts for it to work and all the connections for hardware

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