Perhaps your hard drive has failed? There is a mode to boot without checking the hard drive. Connect to computer with usb when off, then hold down the lower menu button (menu down) all the time while switching on.
Otherwise the standard reset procedure is to hold the X button for longer than 20 seconds.
Fredc thank you for the quick replay !
There is a big chance the h.d has a problem , it was giving errors for some times.
So i was trying to press this 2 buttons combination while the AV500 is conected to the pc with usb but no luck..
It is totally not responding... Is there other way to Install on it the operating system>?