Radeon graphics cards aren't optimized for shaders.
They run best on Nvidia.
That said, you should still get decent framerate with that card.
Make sure your drivers are up to date.
You can use
Driver Booster 3 which is the only driver install software I trust not to carry malware.
Just read carefully while installing. It tries to trick you multiple times into installing other software you don't need.
Your PSU should also be enough.
Have any other programs running?