Power led of my gpu flashing..

[EarthDog]

It may be... did you ever think to test it to confirm either way instead of categorically denying your 7-8 year old PSU with old style power distribution (not all of power on 12V) that wasn't a particularly well reviewed unit in the first place is still smooth as silk? You asked us...remember?
If the light is on, most would logically think to test it instead of think the card is faulty. Just because its on and working, doesn't mean its wrong. It just means the power coming in isn't up to spec for the GPU (whatever that means... ripple/noise etc...). Its just odd that you come somewhere and ask for advice, then crap all over it while, respectfully, you have no idea about these things..

GL to you...

 

[sneekypeet]

....Have you ever thought that maybe Gigabytes sensor is crap?

Then RMA the card and be done with the questions. From the outside it appears you would rather argue than move towards a solution. Both ends of the issue have been addressed. You can either remove the card and RMA it, see if the new card does it (if they find a fault in it.) The other way to go is to try a PSU and see what shakes. No other answers are out there, there are not any other ways to look at it, outside of a possible outlet issue.

You came in not wanting to buy a PSU, so RMA is the only obvious choice. You could go to a big box store and get something to measure the outlet to be certain the issue lies in the PC, at the same time, I feel like this thread is soon to be closed.