Amd drivers problem after install.

Hello, I have a problem after install drivers;

-I can't play games

-My computer running slow

-I can't watch videos on YT in 720p Full Hd in ful screen

-When moving windows(no system) with programs

My specs;

Notebook-Lenovo z-51

System-Win 7 64bit

Graphic Card-Radeon R9 375m

Ram-8GB

History of issue: Last week I bought a Hurtworld .Everything was OK but in setting i forgot to change RAM Bone from 4 to 2. Then my NoteBook was crashed in evry try to open windows normal it just shot Blue screen with STOP 0,00000116x and atikmpag.sys .I know it was problem with graphics card .Next day I removed drivers for this card installed from setup in C/drivers/AMD VGA Drivers/setup .After reinstall from this setup everythink works but it had issues that i mentioned above. I try to install older drivers nevest but no helps.

Sorry for Bad English please help