Help! System cut out completely! PSU?

Hi All,
Logged on with my main machine this morning and was browsing happily when the whole machine just died on me.
It was as if I'd turned it off at the wall plug.
So. I checked my connection from the electricity supply to the PSU, changed the fuse on the plug. Still no good.
I took the side off of the pc and tried starting again. The interior fans give one feeble kick (eg on the HSF), the 200mm exhaust fans on top of the case actually begin spinning but no sound from the GPU, PSU etc, no post.
I have got a blue light and a couple of LEDs on the motherboard that light up.
If I disconnect the power they go out so I am presuming that power is getting into the machine.
Anyone any ideas about how to troubleshoot this?
The PSU is just over a year old (Be Quiet Dark Power 850watt) so I'm hoping it hasn't failed but it certainly looks like it.
I'm at work now so won't be able to respond for another 5 hours but I'd appreciate any suggestions.
I can't afford another PSU right now so I'm hoping it hasn't failed.
There was no noise/smell etc. Completely no warning signs.

Thanks in advance, John

Try stripping your system to its bare essentials - one stick of ram, onboard graphics and no peripherals. Does it boot up? If so, add in the remainder of the components one at a time until it fails to boot. Double check by removing the last component you tried and testing again. It is possible that one of your components has failed and is causing one or more of the power rails to be shorted. Yet another possibility is a stuck switch - have you checked that both the reset and power switches operate correctly?

Normally if a power supply blows you will get that burnt wire smell, but not always. On a modular supply you can also lose one of the rails but the others keep going. You could try moving the plugs around. Otherwise if you suspect a faulty PS the first test is to put another (spare) one in and test. Can you get your hands on a loaner?

That behavior can be caused by overloading the power supplies "circuit breakers", which could happen if a component is shorting out or producing a current spike as Dwarf suggests, and stripping the system down to the bare minimum and testing the parts one at a time is the best way to test for that.

You have a modular supply with four 20A - 12v rails. You want to be sure to "balance" the voltage draw across those rails - don't try to pull all 12v from one or 2 because it looks nice.

More on this stuff at Wikipedia: Power supply unit (computer) - Wikipedia, the free encyclopedia

• The ATX12V 2.x and EPS12V power supply standards defer to the IEC 60950 standard, which requires that no more than 240 volt-amps be present between any two accessible points. Thus, each wire must be current-limited to no more than 20 A; typical supplies guarantee 18 A without triggering the current limit. Power supplies capable of delivering more than 18 A at 12 V connect wires in groups to two or more current sensors which will shut down the supply if excess current flows. Unlike a fuse or circuit breaker, these limits reset as soon as the overload is removed.
• Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[5] both for cost reasons and because it is an irritation to customers.[1] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)

But I also notice you've got a serious overclock on the 920. If the other suggestions yield no fruit you may also try resetting BIOS defaults to test. Overclocks can run stable for a long time and then fritz out for any number of reasons as the machine ages. Worth a look.

More if I think of it!

PSU tester?? Newegg.com - power supply tester
Fabe

I have this one from Antec. Simple inexpensive.

http://www.antec.com/pdf/flyers/power_tester.pdf

Thank you all for your suggestions. I shall work through them, although probably not until I have more time,. This will probably have to wait until the weekend now as I am on long shifts this week.
I have found the manufacturers handbook and this tells me I have a 3 year warranty on the PSU but I'm frantically trying to find the receipt at the moment.

Thanks again for the suggestions.I will repost when I have resolved the issue one way or the other' John

The bad new- I tried everything you guys suggested and it seems the PSU is dead, can't find the receipt or packaging or remember where I bought it from!
When I built the pc (October 2009) I used primarily Overclockers.co.uk and Scan for the components. This morning I rang both those companies and I didn't buy it from either of them.
In desperation I tried two more UK retail sites with no luck,
Out of desperation I rang CCLonline.co.uk, a company I had thought of using a number of times but didn't think I ever had.
The good news- Bingo, they had indeed sold me the PSU. The guy explained that it was out of their 12 month warranty and would have to be RMAd to Germany.
I explained that I couldn't find a receipt or the packaging. He said, no problem just take it out put it in a box with some bubble wrap and send it back to CCL and they will RMA it for me.
This is going to take about 4 weeks but I was thinking I would just have to take the loss and buy a new PSU.
So a big up for CCL! I really think that's good service. Most companies would have left me arguing on international phone calls to Germany.

Thanks to all of you who took the time to advise me Still a bummer but it's turned out alright, especially as they no longer make my model and the replacement will have to be a 900 watt unit that's won loads of awards.

Cheers, John