Why my iMac does not Turn ON?

I have been using my imac for a year.

Yesterday I tried to turn on the machine without any success.

I only hear a short noise if I have my ear in the side of the optical drive and after that a fan working (low noise). Nothing else after that, the screen remains off.

There is only one green LED at the lower part of the iMac.

The only way to turn off the fan is by forcing a shut down with the power button.

The aforementioned LED remains off after shutdown.

I removed the power cable, check the source voltage, tried another outlet without any luck.

Help please. Thanks