I was running my pc through the hdmi connection on my gfx card nvidia gt430 but it died so i couldn't get the display up... i brought a new gfx nvidia gt 630 and replaced my existing one... it boots up but i can't get onto system recover (f8) so Im stuck at bios.. I can't run on the onboard gfx as i don't have a standard monitor to install the old gfx card drivers. all fans still work and the hd was fine before the old gfx card crashed.
Im currently running a emachine E4210 with a 2gig ram
Your power supply could be too weak to run the new video card, especially in a emachines which are known for their bad power supplies and cheap motherboards.
Try getting a monitor and use the onboard video once you remove the GT630 and see if it works fine then. If it does, you should look into getting a better power supply, although for a P4 system, you may just want to save a bit and get a used Core 2 Duo or Quad core.