PC will not start up

  Marko797 05:43 20 Jul 2009

Problem with desktop, will not fire up at all on pressing main button. No noise, no fans, no lights, etc. Have done 'hand n eye' checks (plug, mains switch, lead connected), but still no go.

Strange thing, router still works though (connected to desktop), internet works, so appears not to be a complete failure.

Anyone have any ideas where to start to find the prob, please?

  gigagiggles 06:06 20 Jul 2009


i assume the router is externally powered from the same or nearby ac outlet.

that leaves two usual suspects: psu and motherboard. the psu is the easier one to interrogate.

  birdface 07:08 20 Jul 2009

lead connected.Make sure that you have not turned the switch at the back off by accicent.try a new fuse in the plug.And if not any of those it is probably the PSU thats gone.

  Marko797 10:01 20 Jul 2009

have done above (buteman), & done a bit of research and carried out following:

1. shorted the power switch, still no go.
2. shorted psu green & black wire, fans start up.

According to what I've read, the latter suggests psu is ok.

So, appears it's either mobo, or cmos battery?

Have looked for obvious damage on mobo & can't see any. Is there a chance this could all be down to the cmos battery?

If it is the battery, then do I have to do something with the bios or something if I replace the battery?

  Marko797 10:03 20 Jul 2009

when 1st started this repair job, the light was on, on the mobo (small green one). Now after messing about testing, light has gone off. Does this provide any clues??

  howard64 10:06 20 Jul 2009

the only way of testing a psu is to connect it to another pc or stick another psu in your pc so that it is testing under load. An industry standard psu tester, several hundred pounds, tests the psu under normal operating conditions. Just getting a voltage at odd cables proves nothing other than the mains is getting through to it. If you have a spare pc try swapping if not buy a new psu it is far cheaper than a mobo or cpu. The cmos battery will not stop the pc booting it will only stop the pc updating the time and date etc. The pc will revert to basic standard settings in the bios if you change the battery but not likely to be your problem in this case.

  Marko797 15:18 20 Jul 2009

OK I think I'll bite the bullet on this & try & get a replacement psu. Currently it's a 475w, but as for brand, not sure. On the psu it says HEC - High Quality Evolution Commitment (?), then Intel 12v. The system is an old AMD 3400+ (no jokes please - it runs like a good'un, or did), so don't have a clue as to what I should be looking out for (rail voltages/molex etc, far too complex) & I have several leads coming off - bit like spaghetti junction - but I do know I'll need a sata lead as that's for my HDD connector.

Anyone able to offer any further advice?

Seems I can get a 475w from Ebuyer for c.£16, which will do me until I replace the whole thing later this year. Thnx.

  Fruit Bat /\0/\ 17:45 20 Jul 2009

If renewing a PSU check:

1. The physical size of your PSU, some are hard to replace due to being a non standard size.
2. The amount of power need from the PSU don't skimp.
3 The correct connections for your equipment

1. Physical Dimensions

Besides the specs and form factors, the physical dimensions are also important factors in selecting a compatible power supply. Here is an outline of the physical dimensions of most standard power supplies:

# ATX: 6x3.5x5.5", HxWxD. Most common. Uses 4 mounting screws.
# Mini-ATX: 5x3.5x5", HxWxD. Rare size. Uses 4 mounting screws. Can be used in a regular ATX case, but often not the other way around.
# MicroATX: 5x3x4", HxWxD. Use 3 mounting screws. Not interchangeable with ATX or miniATX.
# Flex ATX: Even smaller than Micro ATX. Various sizes according to case specs; often not interchangeable.

Use the data above to determine if a particular power supply would fit your case.

The quality of a power supply can be estimated by its weight. While this is not a true scientific or thorough measurement of the power supply reliability, it is nevertheless a very simple and easy way for ordinary PC users to estimate and compare the quality of a power supply. Why weight matters click here

2. Power supply calculator click here

3. Correct connections
Some boards have 20 pin connectors others 24 pin
There is often a 4 pin plug required to power Intel CPUs
Molex D plugs for IDE HDD and CD/DVD drives
SATA power connections for latest HDDs and DVD drives.

Guide to changing PSU
click here
click here

  Marko797 17:59 20 Jul 2009

cheers for that.

I think I've got the gist of this now, but a little concerned that I have 3 purple 'molex' type connectors as well as the white ones. Currently 3 whites are connected and have about 6 spare, which seems a hell of a lot. The rest seem fairly routine; sata, dvd/cd/floppy/main 20 pin connector.
Guess I just need to make sure I get the right type of psu, and that it fixes the problem. Not fully convinced as yet, but suppose it's either the psu or the mobo. Don't want to shell out too much on the old rig, you see.

  Marko797 10:50 27 Jul 2009

Ordered new 500w psu Friday from ebuyer on 5 day delivery (£21 incl. delivery), arrived this morning. Just fitted it. Switched on, powered up! Yee-ha - the old rig is up n running again. Thnx to all for advice.

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