Thanks for the suggestions, personally I have no more time at the moment to try the old drivers but I remember trying different catalyst drivers in the past, all versions untill the latest adrenaline ones today. None of them worked for me sadly. I hope this can help others users though.
I come back at times to see if someone have some better workaround or solution. Feel free to suggest me or to share it to AMD in any way. Thanks.
Remembering, some 260x come with the power cable type molex to 6pines. Maybe the problem is that, it's just an idea. It could be tested with a cable from the power source, and not the included cable from the graph.