old desktop wont start up - what to do?

unwashed potato!

unwashed potato!

unwashed potato!

Soldato
Joined
12 Feb 2006
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Surrey
it powers up for no more than 0.5 seconds, just enough for the fans to spin.

any thoughts what we can do to try and diagnose the issue?

it's been sat un-unsed for about 1.5 years now unplugged. even then before that was just for light use infrequently.

have removed anything unnecessary, so taken out the pci usb ports, the gpu, and there are no disc drivers.

just 1 hard drive plugged in, 2 sticks of ram, cpu and nothing else.

still makes no difference.
 
Unplug psu from everything apart from a molex fan. ‘Jump start’ the psu using the paperclip method (loads of YouTube vids) and see does the psu stay on. Could be it tripping out.
 
Could be mobo or PSU.

Try using a different PSU to test it.

Often it's the PSU but don't bet on it and buy a new one, rather just borrow unit.
 
Have tried to jump start the psu with a clip and it worked, so not the psu.

What next to try?

What's weird is that I press the power button on the pc, nothing happens, then I can try to remove the main psu cable that connects to the mother board, and when it's being wiggled it might flash power up for half a second, as though its got a bad connection.
 
Last edited:
Higher Than Average said:
Have tried to jump start the psu with a clip and it worked, so not the psu.

What next to try?

What's weird is that I press the power button on the pc, nothing happens, then I can try to remove the main psu cable that connects to the mother board, and when it's being wiggled it might flash power up for half a second, as though its got a bad connection.
Click to expand...

It doesn't mean you don't have a bad psu still, just that there's power there, a PSU tester would confirm that mate. I think they're about a tenner,saw one at £9. Could be mobo ,I think I'd get a tester next day delivery.
 
Have you tried bypassing the case power switch and jumping the connectors? (head of a flathead screwdriver will do).

Any capacitors on the motherboard look a bit bloated or swollen compared to other identical capacitors close by?
 
t31os said:
bypassing the case power switch and jumping the connectors
Click to expand...

tried it now and it did absolutely nothing. i still find it odd though that the power cord that goes from the psu, into the motherboard, when wobbled, will power the pc for half a split second, the same as what we had when a couple weeks ago the power button did work, which it now doens't at all.

t31os said:
capacitors on the motherboard look a bit bloated or swollen
Click to expand...

nope all look ok.
 
Could be a short somewhere inside the case, tested it outside the case? (on a box, etc) bare essentials, but outside of the case.
 
do all psu fit all motherboards? i just tried to use my problem pc psu to plug into my other desktop motherboard to see if it'd start up, however it didn't seem to want to go in. i was reluctant to force it, and the shape of the pieces seemed to be correct, but i wasn't sure.

how would i know?
 
I've bought a psu tester.

When I plug it in, there are many readings on the digital screen, however the one labelled +12v2 is flashing and beeping every 1 second, with a message saying L.L

From googling people say this means the psu is bad, however when I plug the same tester into my working fine pc, I get the same message.
 
Emlyn_Dewar said:
Can’t say for your PSU tester, but as long as the desktop is standard ATX then any PSU will fit. What spec is it?
Click to expand...
It is atx as the tester works for both my old and new psu, I guess i just need to force it a bit more.

The tester reads as follows if anyone knows what it means.

-12v
12.1

+12v2
12.2

5vsb
5. 1

Pg
310ms

+5v
5. 1

+12.v1
12.3

+3.3v
3.3
 
I have made some progress but feel no closer to sourcing the issue.

I'll try and simplify it with old pc (about 7 years old) and it's components, and new pc (about 2 years old) and it's components.

Old pc at first, you click the case button, it'd start up for half a second, fans spin, then instantly off.

I test the psu cable that plugs into the motherboard using a bobby pin, and it runs fine.

I now plug that same cable back into the old pc motherboard and it no longer responds at all when I push the case button.

I purchase a psu tester, and it appears to be working fine on my old psu, and I try with my new pc psu, also working fine.

I tried plugging the old psu into the new pc motherboard, and everything starts up and runs perfectly fine.

I tried plugging my new psu into the old pc motherboard, and now the old pc does what it originally did, runs for half a second, and then instantly turns off.

Now I'm thinking it's related to the old pc case button, but I confirm, with the new psu it works fine, and even jump starting the motherboard by using a screwdriver on the 2 pins, this works, but, only when using the new psu, plugged into the old motherboard. If I plug the old psu, into the old motherboard, I get absolutely nothing.

That I don't understand, given the old psu, when plugged into the new motherboard, functions normally.

I've unplugged everything from the old motherboard, other than the cpu, and it still does the same thing.

I've changed the battery, as the old pc was left unused for a long time, at least 2 years since its last use, but that was just a short 2 weeks use, before then was probably another couple years.

The battery however isn't the exact same size being a smaller capacity one, however googling says it'll still work.

So now I'm stuck.

Why does the old pc not get any response from the old motherboard, while the new psu does get a response from the old motherboard, but then why is the response just to start for a split second and turn off.

What do I do now?
 
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