Power Issues?

Right, I built a new system for a friend last week, spec as follows;

ABIT IP35
Q6600
3GiB RAM
300GiB HD (taken from old machine, PATA drive)
GeForce 7600GT (taken from old machine)

He had an FSP 400w PSU which I'd used in the build of his previous machine a few years ago, I made the decision to swap the PSU out for my Corsair HX520 so his machine would have no issues - assuming the 400w FSP would power my system ok (see my system).

Now, as it turns out - this doesn't appear to be the case, the PSU claims 80% efficiency so its actual power output when new would be a max. of 320w, which doesn't seem to be enough for my system on boot - it keeps turning on and then off after a few seconds - these bursts of life are for maybe a few seconds at a time and then thats it.

Am I right in diagnosing it as being a PSU issue?

If so, I'll get him to buy a new HX520 and stick it in this machine!

Well one way to find out is to get your HX520 back for a test and see if it fixes the issue

Sounds like a definite contender but usually the PSU would die in this situation, im surprised it showing " bursts of life"

Are you sure all power connections are secure?

It sounds like it could be the psu, you say this had been in a build you did a couple of years ago, well psu's deteriate over time, so it may not even be pushing out the 320w.

You could try disconnecting things like dvd drives, floppy drives, any hdd (except your boot drive of course) this may enable the machine to boot as there is less stuff to power.

You could try replacing the corsair hx520 into your pc, to make sure it is still able to boot, if it does, get a new psu.

Just as a side note, 80% effeciancy doesn't mean that it'll generate 80% of the listed rating, it means that it's 80% effeciant at conveting the electricity in the wall to the rated spec.

E.g. 400w PSU at 80% effeciency draws 500w from the wall.

Your 8800GTS OC is probably eating too much power from ther 12V rail. Most if not all PSU from 3 years or order generally have a much lower 12V rating.

Consider the PSU still manage to push your system for a few seconds it seems to be just on the fringes of overloading (I reckon something like 130% load, just rought guess)

With just a 7600GT I reckon the old PSU will handle his system just fine.