iMac 27" (2013) is switch off but fan run at full speed

Hello to everyone,

I have this 'fan runs when I power down the iMac' issue with my 2013 27' iMac purchased in January.

My Imac has worked flawlessly until yesterday, after a few days ago I started to use the usb hub (powered USB 3.0 4 ports hub).

Yesterday morning after working normally I put the iMac in standby mode (menu apple-stop); yesterday evening I try to wake up the iMac with no responses. I tryied to shut down by holding down the power button without any results. At the end I unplugged power cord, at which point the fan starts to rotate at high speed, stopping only when I turn on the imac.

After that the imac works on a regular basis when turned on. Then when I turn it off (apple menu-shutdown) the fans start again until I pulled the plug.

I tried resetting smc and pram, without success.

Here

https://discussions.apple.com/thread/4628811?start=15&tstart=0

I find more guys with similar issues...

Thanks in advance for any help,

Daniele