Computer runs horrible after upgrading to Windows 7 32xbit.

yesterday I upgraded from windows XP to windows 7 but after installing all my drivers I can only get around 15 fps in league of legends where i used to get 50-60 at all times. Same goes for every game I've tried after upgrading. System specs for those interested: Sapphire Radeon HD6870 Intel Xenon dual core 3.20ghz 4gb of RAM