Geforce 8400 GS graphics card question?

I recently bought a Geforce 8400 GS PCI graphics card for my computer, to replace the AGP card I had so I could run some applications I couldent prior. After I installed the card I began to notice that when playing some facebook games like Cafe world or Empires and Alies the game would run really slow and or freeze up, Also my video when watching on netflix is lagging and choppy as well, it starts playing good for a while but then the video stops and the audio keeps going, Im very aggravated by this and would love a solution, I have a gig of ram in my computer and 350 ATX power supply, which should be ample power. does anyone know how I can fix this problem?