What is your PCie expansion slot version (1.0 x 16, 2.0 x 16, 2.1 x 16, 3.0 x 16)? I had to upgrade my 250 watt psu just to run an HD 4350 with 2gb of extra RAM on mobo. I put my R7 240 into a PCie 1.0 x 16 port and it works just fine, if you want to get the most out of any new gpu you need 3.0...