Nvidia Graphics Card Issue

Hello,
I just purchased a brand new Nvidia Geforce (BFG model) 8400 GS 512mb card for my computer. As of now I have a Geforce 6200 128mb video card and its working perfectly well. I decided to upgrade because I enjoy playing games and I want to obatain the best graphical display as I can. I unistall the old Geforce 6200 and shutdown the computer, pull it out and place the newer Geforce 8400 GS into the PCI slot. I go on to turn on the computer and it displays the DELL starting up screen but then goes to a blank screen after that. I tried calling techy support and ended up waiting out on hold twice. Ive considered updating my BIOS but I hear its pretty risky if you dont know what your doing. And yes, I have gone into the BIOS and enabled PCI slots. Any help? Please and Thank you :]