The humming coming from my receiver is driving me crazy! It is a
50-60Hz humm that is constant in volume (it does not matter if I turn
the volume knob of the receiver.) I've tried disconnecting the signal
source (my PC), turning off all the equipment around, moving the
receiver / speakers to another house but nothing has worked. Can
anyone help?

Is the receiver itself humming, or is the hum in the audio signal that
goes to the speakers?

In other words, do you hear the hum from the speakers?

Have you tried disconnecting everything from the receiver, including
the speakers?

If you then reconnect the speakers to the receiver, do you hear the
hum?

Is there a powered subwoofer in your system?

I think there are two possibilities:

* Ground loop somewhere in the system. Search the web for comments and
solutions.

* Your receiver is defective or failing. Take to repair shop.

You could also ask here for advice:

rec.audio.tech

I'm crossposting my response to that newsgroup.