FPS Drops every 2 sec, help!

Hi, my brother gave me a Geforce 9800gt and i put it in my computer, and after that my fps have been dropping every 2 sec, its not playable with this since i get freeze lag every 2 sec, can someone tell me how i can fix this problem ? :P

either your psu (power supply unit) has a too low power or your pc has a to high temperature. check your pc for dust on the hardware and clean it (often helps a lot!) but i think the psu causes this.