Games not running as they should

Hello everyone

i got a problem with my new pc, Basically i cant really run any "new" games or old for that matter without having FPS problems (even with everything on low graphics)
i play stuff like Diablo 3 , starcraft 2 , Guns of Icarus Online , and alot more games
the pc i had before could run all my games no problem , and that was alot worse then the one i have now

so pls help :)
(btw all my dirvers are up to date)

Specs

Windows 8 64bit
AMD A6 3620 quad-core processor
AMD Radeon HD 8470 2GB
1TB Hard Drive
16GB DDR3 memory
and i got bullgaurd for antivirus