When you mentioned that the GPU Fans used to run during POST or when first booting up this is normal since BIOS is checking your GPU Card.
But now you mentioned that the GPU fans DO NOT RUN at POST like before. This is not a software issue since at boot up there are no software loaded since Windows hasn't started loading up yet. It is just BIOS running.
So you have a hardware issue with your GPU card. I would check the GPU card for any damage or discoloration. I would also physically check the Fans on the GPU and its connection to the GPU if possible without taking it apart.
Check to make sure both PSU Power cables to the GPU card has a good connection. A loose PSU power cable can prevent the fans from running.
If you don't see any wrong I suggest your open a RMA Ticket with the Manufacturer of the GPU card and have them check the card out for you.
To eliminate your PC as the culprit I would test your GPU card on another PC, either family or friends or computer shop, to see if the same thing occurs. If it does then you most likely have a defective GPU Fans or card.
