need help upgrading graphics card for 240 watt psu

I recently purchaced a power color 7770gpu for my alienware with 240 watt power supply. I heard it was a good upgrade but when I install the graphics card in my computer it wont even cut on my monitor , even the integrated graphics wont work with it installed but if I put my old gt545 back in everything works fine . I sure would like some advice on which way to install this graphics card because I dont think its cutting on at all and yes this is my first graphics card upgrade.