View Full Version : Help! PC won't start after power cut

30th December 2014, 10:05
Been stormy all night and day and the mains protection cut off the electricity.

I know the bios battery on my PC does not work but usually after a sudden power cut the PC boots up again with default bios settings.

Now it won't boot at all. I press power on and all the fans turn on and the light on the mobo turns green but nothing else.

The fans of the GPU are remaining at full blast (it does that normally only for a few seconds when switched on)

I tried disconnecting the power and resetting the bios but problem remains.

Mobo is an ASUS P5K SE and CPU is a Q6600 (Quad core)

30th December 2014, 11:13
Well, first of all I sympathise with you, as I've had many a electrical product die due to power cuts, as we live right next to a distribution unit which regularly cuts our power for various reasons (some initiated by the grid contractors).

things I would think of are as follows:

1). Do you get any bios POST audible beeps at all when the unit powers up? This will help identify if it's something external to the motherboard itself, such as a memory module, GPU card or other card that may be causing the motherboard to mail POST processing.

2). Assuming you get no audible beeps as above, I would strip the motherboard down to nothing, meaning remove each and every component and the power feeds, and the CMOS battery. I would take the opportunity to replace the CMOS battery at the same time since it only costs about a pound to replace, and I would see if the motherboard manual states if there is a CMOS/BIOS jumper settings reset option (which I acknowledge you allude to when you say you reset the bios settings, but for clarity it's worth rechecking and redoing), and I would reset these settings with the CMOS battery removed.

3). Once done I would pop the new CMOS battery in, CPU in, the least amount of compatible memory in its correct allocation per slot and then connect the power and power it up without anything else connected.

If it doesn't work after the above, it's likely that the motherboard is duff. Since it's more likely that the motherboard is damaged rather than the CPU, I'd start with replacing or repairing the board.

Just to clarify also, unless you have a modem card connected in your PC (since storms can cause a surge through the modem line, into the board), or have ADSL connected, then I would likely think the culprit was that the PC wasn't unplugged when the power cut off, and then was turned back on when the power came back on, thus allowing a surge to pass through to the motherboard.

Therefore my advice would be (to anyone including myself as i always do this with equipment, including TVs) to always unplug the equipment during the power cut, then once the power has come back on, plug something simple into the power sockets and test, such as a small lamp. This will ensure that any surge is passed through to an object you won't mind losing, and will hopefully just result in a fuse blowing rather than anything more serious. You could also try only loading up each breaker switch one at a time Rather than turning them all back on at once, which can cause more trips. Once your happy that the power is stable then what I normally do is remove the excess power from any capacitors on the PC board by powering it on without any power plugged in, and then you can plug it in and retry it.

This isn't a "cure-all", just best practice.

Afterwards, I would buy yourself a UPS to protect and allow you time to shut down the PC if a cut occurs, whilst giving you surge protection when the power comes back on.

Hope you get it sorted

30th December 2014, 11:57
Thanks for your reply Trapshot and very interesting stuff.

I've sorted the problem and its now working fine.

First, I tried another PSU but that wasn't it.
Next, I tried another graphics card, but that didn't do it.

I read somewhere on the net that it could be faulty RAM. So I unclipped one of the DDR2 sticks (it has x4 1GB sticks) and VOILA! It started up, but of course with only 3GB RAM. Luckily I had a spare DDR2 1GB RAM stick (identical to the old one, same make/model/specs).

Seems with these boards that they don't beep if there is a memory problem. The RAM stick is a Corsair. Aren't they supposed to have a lifetime warranty ?

Also, is it possible the surge destroyed a ram stick but nothing else ? I remember yesterday that the PC was running really slow all of a sudden, even after a reboot. Its running fine now.

30th December 2014, 14:04
Glad you got it sorted easily, always a relief!

Yes it's possible that just a stick of RAM dies, I had a stick die on a server earlier this year from a similar issue.

It's all down to whichever component is most worn or least well resistant to the surge, so it could be any component ultimately.