Omg I suppose u are a noob!
xD How is your PSU? The downclock means probably that the VGA hasn't enough power supply. I've got a 4870 and it's a beast, but it's really greedy of energy. So I suppose u have to change your PSU with a etter one!
Oh, you can't, YOU CAN'T stay with that version of the drivers!!! Make them work!!!