Inspiron 570 video card issue

Hey, all

I want to install a 1GB NVIDIA GTS 450 in my Inspiron 570 desktop. However, when I tried to do so, I booted up the computer and was greeted with...nothing. No display, no startup, nada. So I've two questions:

1) Do I have to plug it into the PSU, and if so, will mine work? The card says it needs 400W, but my PSU is the default one (@300W)

2) Would installing the drivers beforehand make any difference at all?

I don't know what else to try. I've used the DVI and the mini-HDMI port and got bupkis.

My specs are:

Inspiron 570

AMD Athlon II X4 630 @ 2.80GHz

6GB RAM

NVIDIA GeForce 310 (1GB)

Win 7 Home Premium (64-bit)

Help? Thanks!