Dell Studio 540s GPU upgrade

Hi,

            I am using Vista and trying to install an Nvidia GPU GT630 1GB . I have have latest Bios 1.1.13 .

The PSU was 250w but changed to 300w for the graphics card . The PC will not boot . I did notice in the Bios that  a setting for video memory size is 128 m  max but is this just for the onboard graphics . I cannot install the driver with the card in the slot .

 Any help appreciated .