Problems after upgrading to ATI radeon 5770 in my mac pro 2008

Day one
I have upgraded my graphic card to ATI radeon 5770 in my MacPro 2008.
4 hours of installing the screen went blank with noice and line, like it happens in telivison when there is no signal.
Day two
Same thing happened when I started my computer.
does anybody know a soluton to this problem?
please help.

Mac Pro community is here.
Did you try Apple Hardware Test by extended testing?
I suppose graphic card is something wrong.