I contacted ZOTAC technical support and told them the exact problem.Here's what they said : "It does not appear to be problem coming from the display card, but from other software / hardware issues.It is possible that the power at the display card is not stable. Please test the card on the same system however with a falling working PSU unit recommended over 500 watts."
Now,what do they mean by testing the card with a 'falling working PSU'?
My mobo has 2 PCI Express X16 slots.it says the blue one is @16X and gray @4X(btw what is the difference between the blue PCIE 2.0 and the gray PCIE 2.0?).Currently i have the card in the blue slot...will it help if i change it to the gray slot and test?then probably i'll be able to check if it is the slot which has a problem...any suggestions?
They mean, I assume, fully working, as in one that you know works fine. Essentially, they have said what we have, however they will swear black is white that their hardware isn't to blame, so they don't have to replace it for you.
If you do put the card in a system that you know fully works (may have to remove all video drivers, then install the correct gtx260 drivers to get it to work) and see if the same problem occurs, they should have to accept it is their unit that is faulty, that is ofcourse, should the problem occur. That is, really, the only way you can be certain it is the issue. It sounds like it most probably is though, to be honest, either that or a software problem, so you can just try to BS them if you want and say you have tried it in another, completely seperate syste, with a fresh install of drivers and what not and it is still doing the same thing. Then they will test it for you when you send it off for replacement, and if they say they found no problems, you are out a few $ shipping, but know that the card is fine, then you can be certain it is either mobo or software.
As to the difference between the 2 lanes, the blue is x16, the grey is x4. Your board doesn't support crossfire, the other PCIe lane is just for another PCIe expansion card, but is best not used as the primary graphics card, because of the lower speed. I don't see a reason why you couldn't use that other lane for a physx card, or a card for if you wanted a 3rd monitor say
=EDIT=
@bigfella
He has a graphics card problem (potentially). It starts out at full performance, however deteriorates after the system has been left on for a little while, and this only started happening after a power cut and driver updates. He has tried reverting to the previous drivers, but that hasn't helped anything. It also seems that it is sporadic as to whether or not the system will have full performance when it boots, as sometimes, it is fine, other times, it is at the lower peformance that it gets towards after being on for a while. Benches show lower scores when the system is "less powerful" and also games have lower FPS.
He looked at his power supply readings from HW monitor and they were unusual, however can't be used as any kind of evidence for a PSU problem as HW monitor, and indeed any other hardware motoring software, is less than totally accurate, as was demonstrated by linkin and myself, as I pointed out I apparently have no 12V rail and a +3.3V rail of 0.53V according to it. He also checked the BIOS, and all seemed normal, so that isn't a problem it would seem.
He doesn't have another system to try it with unfortunately to test, however because of what has been said it would appear to be either a GPU, mobo or software issue
now you know
and full software specs are in first post.
all of that could have been found out from reading the thread though to be fair
somethings bound to go wrong.