Zotac nvidia gt630 2gb ddr3 graphics card ...problem.

HI, Just bought a Zotac nvidia gt630 2gb ddr3 graphics card. earlier i was having a Asus nvidia 8400 gs 512 mb. Now when i switched the cards and boot up the system it hangs on to the boot up screen though i can hear the windows starting up sounds but there is no video. i have also changed the psu to 450 watts, the recommended psu for this card is 300 watts, but nothing clicked. when i put back my old graphics card the system boots up fine. is it possible that i got a faulty graphics card? my system specs are : intel i3 3.10 ghz, 2gb ddr3 ram, 500 gb hdd. please help as i have no clue whats wrong my system.