Need help fixing my first PC build

[whitescar1000]

Hello guys I am really having problems fixing my PC I built back in last February. After I managed to put it together, everything was working fine for about a week or just over. After that when I tried turning the PC on it would switch it self off after about 3 seconds, then about 3 second later turn it self on. Next day I tried turning it on it switched it self off right away and wouldn't turn on again. I had the power supply replaced but that didn't work.

So I handed the PC over to someone I knew that had testing equipment, after months of waiting I found out the problem was a ATX PCB Power filter controller failure on the motherboard. So I sent the MB off to be replaced, and got a new one last Tuesday. When hooked it up and turned it on I got two problems.

One I get no video signal on my monitor and the VGA error light comes on, I have tried my gtx 520 which worked fine on the first MB before it failed and I then tired it on my new 680 which I which has never been used and still no signal. Also tried the on board gpu on the MB but again nothing. I know the monitor works because I tried it on my laptop as a second monitor and its fine.

The second problem I got was the PC was turning it self off again about about 3 seconds after I turned it on and turned it self on again. So after 24 hours slamming my head against my wall I set about trying to to find the issue. First I took the MB out of the case and placed it on the box, took the power supply out and turned it on, clean boot up but no video signal. So then I hooked up the lead from the case for the power and reset button to the MB, but keeping the power supply and MB out of the case still and again a clean booted up but again no video signal and VGA still coming on. I would also like to add that while I was doing this I had the CPU RAM and video card in the MB.

So thought maybe the case had some sort of grounding problem that was causing the problem. So I installed the the MB back in the case while leaving the power supply out of the case and hooking up and powering the system up from the case, again clean boot up but no video signal. Then tried with the power supply in the case, then with the case LED's, then with hard drives connected, clean boot up.

So, why is it that I have issues powering up the PC with the first MB and with the second but now I took the MB and supply out, ran it, then put them back it am I not getting the problem any more? Will I get the same issue again in a weeks time? Also why is the VGA error light coming on and why am I not getting a signal on my monitor do I need to RMA the MB again Do i need to RMA the case?

I have spent over £1200 including a £400 video that I have yet to use and had been gathering dust since April, kind of a shame.

Please help

 

[SouthEastBlue]

Have you tested the PC with a different power supply, or tested your power supply in another system? If it's booting on and then off again like the previous one then maybe the problem is the power supply...Also if there's no signal then maybe it's not powering the graphics card correctly either.

Have you tried each individual ram stick in each slot on it's own, to rule out faulty ram also?

Also just to be sure, is the motherboard 8 pin CPU connector in its slot, and same for the 24 pin motherboard connector?

 

[whitescar1000]

I don't have a different power supply at the moment, but like I said the power supply was the thing I replaced and it didn't fixed the issue. I have tried different RAM sticks in different slots and the only time I got an error from those was because I did sit the sticks correctly, other then that they seem to be working fine. And yes both the 8 pin and 24 pin are connected. I have also tried looked at the CPU, checked the paste the socket pins just to be sure.