Most definately your power supply is the root of your problem. Here is the Power Supply chart everyone references when buying a PSU http://www.computersoc.com/viewtopic.php?p=37606
I would suggest a Corsair, OCZ, Seasonic, Antec, or PC Power and Cooling brand. Here is a nice one that would run a 4830 and the rest of your system easily and its a 80+ which means its very efficient on electricity
Antec Earthwatts 380W $40 shippedhttp://www.newegg.com/Product/Product.aspx?Item=N82E16817371005
And here is one I would recommend if you are planning on keeping this power supply for your next build. This would run a Core i7 and a nice system.
OCZ StealthXStream 600W $80 shipped, $50 with Mail in Rebatehttp://www.newegg.com/Product/Product.aspx?Item=N82E16817341010