Still having issues booting my desktop!

[Gideon Lorr]

System specs:
Q6700@stock
4GB DDR2
ATi 5770
Gigabyte ep45 motherboard
OCZ ModXStream Pro 600W Modular
All parts four years old.

My desktop is having huge problems turning on. In summary:

1) Switch on, odd fan noise.
2) No signal through to my TV, and seconds later, the machine powers down
3) It then starts up again.
4) Repeat steps 1&2 up to ten times
5) Picture signal on my TV on boot #X, machine boots successfully. Once up, no issues (though I've not tested any games)

So I'm fairly sure it's the PSU. But are there any sure fire ways of testing this? Software, or measuring voltages?
I've swapped out GPUs to no effect, removed my wireless card and replaced with a Virgin Media dongle (both keep dropping out).

I'll have a go at swapping out ram sticks to see if any of those are bust. Though surely if one was broken, the system wouldn't boot altogether?

Any help is much appreciated, as I'd like to order the parts ASAP!

To follow on from this, I've swapped PSUs, and I'm still having the same problem.
It isn't my GPU (swapped that out).
Nor my wireless card (switched to a dongle)

Need to double check memory sticks, swap out CMOS battery, and also use the power button on my mobo to ensure my case power button is not shorting.

Otherwise, I'm thinking possible HDD failure? I've disconnected my secondary drive, and I'm still having the issue. I've ran the appropriate Seagate diagnostic tool on my primary which hasn't detected any problems, which makes sense as once the machine successfully boots, I'm having no problems.

I have a Vista installation on a HDD from an older desktop- should I connect this up and see if the system works?

 

[Gideon Lorr]

Anyone?
I've found a spare HDD, formatted it, and installed my OS on that. Updated it smoothly, and powered it down.

When I powered it up, the same problem again. So now I'm at a bit of a loss.

 

[OracIe]

Go back to basics.

Unplug everything all bar the essentials (Power, RAM, CPU (Assuming you have onboard GFX, use that))

CMOS reset

Try from there.

To me it's not necessarily the PSU but it sounds like on initial startup, the BIOS is making a configuration change and then restarting.

Have you tried to replace the BIOS battery? Is there a BIOS update?

 

[Gideon Lorr]

Right I've reset the CMOS. No effect.
Switched the CMOS battery: no effect.

I've tried all my ram sticks (four) individually. System booted fine with each.

Tested in pairs. A couple of combinations led to the machine not booting. When I retested them, the machine booted just fine.

Very lost now.

 

[biuro74]

There's one explanation when some issue seems to arise suddenly, with no "visible" reason. Metal sockets and pins are vulnerable to slow oxidizng/verdigris during long time. If PC is 4 years old, and is present in such humid environment like UK is, it is possible. So when "suddenly" something stops working fine - it doesn't have to be broken.
Sometimes just taking out components and putting them back helps as when you pull out any card from its socket (graphic card, memory stick, even SATA cable), oxidized layer gets off by abrasion - so once it's put back it might work properly again as the electrical connection is restored. Sometimes interfaces need to be cleaned which helps a bit, so bear it in mind
I don't tell you what's wrong with your PC - just give you an option to check.