New PC Gamer Needs Help Upgrading PC a $325 Budget?

. I have a HP p7-1054. I am switching to PC But I don't know much. I am thinking ASUS Readon HD7790 but I don't know if its too much for my PC or could I do better for that price. I also need a power supply I think of getting 650 W corsair. But I hear they have a problem with bussing noises and I get annoyed easily lol. Should I even consider getting a new case. Please give recommendation. Remember $325 dollar budget but it is flexible. Game I wish to play - tomb raider, Bf3, Crysis 3(medium-high settings), SC2