Question My PC doesn't turn on with the new PSU ?

[MichaelKnight]

I have a very old pc:
Gigabyte x38-dq6 motherboard
Intel quad core 2.4ghz(I forgot its exact model but it should be from the first quad-cored cpu series of Intel)
4gb ddr2 ram
Nvidia Gtx970 graphics card

A few weeks ago, it suddenly stopped turning on. I thought it seems like a psu(coolermaster v750 750w) problem and tried it with my previous psu(cooler master extreme 600w, it is a working psu but it's fan had stopped working).

And it worked, pc got turned on and all the components were working.

So I ordered a new psu(Silverstone da850 850watt).Now the problem is, again pc not turning on. If I switch to my oldest psu(coolermaster extreme) , it works, but when I reconnect the new psu, pc doesnt work, not even turns on.

I think the new psu may be DOA. Is there another possibility? One thing I noticed is that, my pc motherboard has 8pin socket for cpu, there are four square outer pin and 4 a bit curved outer pin.My oldest psu has 4 pin cpu from a rail and another 4pin from another rail and it has 4 square outer pins and 4 curved in total. But my previous psu has 4+4pin cable and one of them has 2 squares, the other one has no squares.I was just using one of 4pins cable not the other 4pins which had no squares.

The new psu has not a 4+4 but a full 8pins cpu cable and has just 2 squares. It can be connected to the socket without using force but may this cause the problem, that the number of squares doesn't match?

I tried the new psu with the previous psu(v750) 's 4+4 cable too, just using one 4pins connector but it changed nothing.

When I connect the oldest psu with fan problem, the pc turns on. I am just using for test the motherboard and cpu connections to psu only.

 

[DSzymborski]

Here's one problem: the Silverstone DA850 doesn't appear to come with any CPU connectors that aren't 4+4; sites with detailed specs and the reviews for the PSU only refer to 4+4 cables and Silverstone's page for the PSU only shows clearly a 4+4 connection in the gallery.

In this case, the only solid 8-pin on the modular CPU cables are the side that goes into the PSU. Modular PSU cables are not necessarily symmetrical. Luckily, it doesn't appear you fried any of your components, but it's possible that you did damage the Silverstone PSU.

 

[MichaelKnight]

Thanks for your answer.

After reading your answer, I was able to seperate the solid looking 8pin into 4+4, though it still doesn't work unfortunately. Can't it be used as 8pins on my pc's motherboard? When you wrote that I might have damaged the psu, do you mean I damaged it by using 8pins on the 4+4 socket of my motherboard or by connecting the wrong end of the cable to motherboard and psu? (actually it's impossible to do the latter wrong, psu's sockets don't allow it)

 

[MichaelKnight]

A few minutes ago I applied the famous paperclip test technique on the new psu and the psu's fan started to spin.

So it seems like the new psu isn't dead.

I noticed that if I try to use the powerswitch on the pc case the new psu's fan does not move(of course still the pc doesn't turn on) , if I use just the paperclip it's fan starts running.

 

[--SID--]

Disconnect the PWR+ and - from the motherboard and try to jumpstart the system by connecting the PWR+ and - header with a screwdriver.

 

[MichaelKnight]

Thanks for your answer.

I am writing this message on my computer.I wrote that I was just using only motherboard and cpu cables and the computer wasn't turning on.But actually "Power Led", "Power SW" and "Front panel USB" headers were still connected to the motherboard.I disconnected the Front Panel USB headers and it worked!

The front panel USB ports had been in accidents in the past and just one of them was still working, actually half-working(sometimes working sometimes not).My previous psu stopped working about a few-weeks ago. Then I tested with the oldest psu and it was working even those usb headers were connected, so I thought it was a psu problem and had bought the newest one.

So actually it was not a psu problem I see, but I am not sure why oldest psu is able to work even when faulty front-panel USB headers are connected.Maybe that psu doesn't have Short-circuit protection and other two have, may the reason be this?

So it seems like I have bought a new psu although it was not the previous psu's fault but no problem because that previous psu is 6 years old and I was planning to build a completely new system(other than the internal bluray burner) in a month and before buying the new psu I was planning to use it temporarily on my current pc and at the same time was planning that it would be my new pc's first component, so I don't regret it.