Dodgey PSUs need help

Hi,
I've almost finished building a new PC but I'm having some trouble with it.

PC Specs:

Gigabyte GA-K8NXP-SLI
480W Tagan TG480-U01 Quiet ATX2.0 SLi 12v EPS/SATA/XEON 3 Years Warranty
AMD Athlon64 3500 Venice Retail
2GB (2x1GB Corsair DDR400 Value RAM) can oc to ddr500
SAMSUNG - 200GB 7200RPM - HARD DISK DRIVE
Ebuyer Extra Value 120mm Internal Case Fan In Black & Antec SLK3000B Black Super Mid Tower Case
OcUK GeForce 7800GT 256MB GDDR3 TV-Out/Dual DVI (PCI-Express)
Pioneer DVR-110D Black 16x16 DVD±RW Dual Layer DVD Writer

As far as I can tell it's the PSU that's causing me grief for some odd reason.

When I first tried to boot up my PC only the front LEDs and Dual Power System card kept flashing.

Also the rear case fan was spinning in both directions but VERY slowly and the heat sink fan too going slow and after a few seconds the PC would shut down.

So I checked the configuration of the power connectors to make sure everything was correct and tried again with the same result.

A friend of mine had mentioned maybe the motherboard was short circuiting and try lifting the motherboard out and try again.

But before that I decided to use an old Qtec 550w PSU I had, the PC booted up absolutely fine and when I tried the Tagan one again it wouldn't even power up.

I just thought the Tagan PSU was just faulty but unfortunately I had scratched the black finish on the PSU quite badly but this couldn't be helped because the Antec case has a support bar for the PSU that goes right across it so I had some difficulty trying to get it in the first place.

But I seriously doubt the damage I did to it would cause it to be faulty at all, so I decided to just send it back to the manufacturer later and get a replacement.

However I decided to buy the same model again because I needed another PSU for my older PC anyway so I tried it in the new PC with it lying flat and the PSU resting on top it and it booted up fine just like before with the Qtec one.

At that time I didn't have time to finish building it, so I just left it like that for a day or two.

When I tried finish building it by putting the PSU in very carefully this time to avoid scratching like before.

I tried booting it up again but it had the exact same problems the previous Tagan PSU caused.

I checked the configuration again and it seemed ok to me but the same thing kept occuring again.

I took the new Tagan one out and tried the Qtec 550w one again and then it booted up fine.

So I'm left at a loss at what to do really, the new Tagan PSU worked fine before but I when I placed it into my new PC it was only slightly scratched so that couldn't have damaged it.

I'm wandering could it be the motherboard or incorrectly placed connectors but that wouldn't explain why the new PC would boot up fine with my old Qtec 550w.

Both PSUs can't be faulty now so I tried the new Tagan one in my old PC and the motherboard LEDs showed it was getting power from it.

But when I pressed the switch to off on the PSU it wouldn't cut off the power to the motherboard, so at the moment I decided not to bother booting up my old PC with it to avoid risking damage.

I might try again later with it in the old PC to see if it can boot up or not.

I'd greatly appreciate any advice since I'm at a loss at what to do to solve the problem.

Thanks.

That is very strange. Is the Qtec an ATX 2.0 with the 24 pin connector? What was the system you were powering using the Tagan. This may be a silly question but you have plugged in the 4 pin ATX plug aswell as the 24 pin one havent you?

Thanks a lot you pointed out exactly what I did wrong hehe, I feel silly now :(.

One friend of mine was telling me I needed the 4-pin connector but another one said I didn't and I got even more confused when the mobo booted up fine with both plugs in from the qtec PSU.

Can't believed I missed out on such a minor thing, thanks for your help!

lol, i almost did the same thing, but questioned why it was so short.

Glad to be of service

QTec? :|

At the time I couldn't afford an expensive PSU so I had to go the cheap route, like 20 quid hehe.

Obviously I wouldn't recommend them for overclocking but other than that they're alright.