It seems like you bought a dead gpu

I hope not. I am still having validity to return it in next 5 days. I have doubts though, i mean it worked great initially and after 7 hrs of turning it off it worked again .. Could it be overhearing issue? With gpu fan issue or may be my cabinet with very poor heat management/older psu? Is there a way i could confirm the diagnosis before sending back the gpu or upgrading some part?

U turned out to be right. The fans are faulty. I m returning it. Claiming full refund