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PC not switching on, stumped....

Last response: in Components
a b ) Power supply
December 21, 2012 3:13:29 PM


I switched on my PC a few days ago, used it fine, then switched it off. Next morning, I press the power button and nothing. The Mobo light was on but no booting, not even fans spinning.

I took it to a PC repair place as I was unsure what it could be, they did a swap test with my PSU and said it was working fine.

I installed a new PSU today as they said that would work and still nothing, Won't switch on, but MoBo light is on.

Im sure its all wired correctly, anyone have any ideas?

Many thanks

More about : switching stumped

a c 124 ) Power supply
December 21, 2012 3:25:36 PM

Go over your motherboard, looking for swollen or leaking capacitors. Google is very friendly, and will provide a lot of images if you search for "bad capacitors."

The mobo light being on just means that it is getting +5VSB.
Swap the power switch and reset switch wires, and then see if pressing reset turns your PC on. If so, you've got a bad or dirty switch. Your case manufacturer may be able to provide a replacement, or you can buy a pushbutton switch and wire it in yourself; you may need to drill a new hole in your case to mount it.
Does any fan even twitch when you try to turn on your system? If so, something may be shorted. Unplug your CPU power cable and try again. The machine won't boot, of course, but if the fans and LEDs power on, you probably had a VRM failure (mobo is toast).
a c 142 ) Power supply
December 21, 2012 3:29:57 PM

To eliminate the switches as a possibility, use a screwdriver to momentarily touch the two PWR pins on the motherboard front panel header.

To eliminate shorts as a possibility, take the motherboard out of the case and then try to power on.

Past that, there is some sort of a defect.

You could try with just one stick of ram, then another.
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a b ) Power supply
December 21, 2012 3:37:06 PM

Thanks for the quick reply,

I swapped the switches first, nothing. No fans twitch when I try to switch it on. I unplugged the CPU Power cable like you said, and the fans started. I switched it off. Then to show the wife I plugged the CPU back in, no start (expected) unplugged the CPU cable again, but this time nothing started when I switched it on. Can't see any damaged capacitors either.
a b ) Power supply
December 21, 2012 3:48:09 PM

Ok, now I have it so it switches on without the CPU Power cable plugged in. Would that mean a MoBo or CPU problem?

thanks again.
a c 124 ) Power supply
December 21, 2012 3:49:29 PM

Check for foreign objects, especially metal (screw, paperclip, staple) on or under the mobo. That it powered on the first time you unplugged the CPU cable, but not the second time, is strange. You say you have a new PSU, so it isn't likely to be the power cable. Reseat the main 24pin power cable as well.
a c 124 ) Power supply
December 21, 2012 3:51:14 PM

Ah, now that it switches on, I'm think it is more likely to be the mobo than the CPU; I've never had a CPU die, but lost a mobo due to a fried VRM earlier this year. The CPU is working just fine in Phoenix now (the PC below, which rose from the ashes of the old one).
a b ) Power supply
December 21, 2012 3:55:58 PM

Nice name for a PC.

Kinda mad at the repair place because I bet my old PSU was fine all along....

Thanks for all the help.
a b ) Power supply
December 21, 2012 4:15:37 PM

Have fixed it now, not sure what it was, but I just tried it again and its working.

Many thanks to all for the help.
a c 124 ) Power supply
December 21, 2012 4:52:53 PM

Bizarre...hopefully just something loose. Glad it's working.