My first question is to power. Check the box of the new card and see what wattage the power supply is supposed to be for it, and then check your power supply. If you're under, or within probably 50W of what is recommended on the box, you need a new power supply.
If that isn't it, then make sure that you have the right slot. There's PCI-E 1.0, 2.0, 2.1, and 3.0. While they may be backwards compatible, the card might absolutely require a specific version slot.
Are you sure you're not hearing the system making any kind of beep code that can be used to help diagnose the issue?
I had recently bought an ATI Radeon 5750 video card to replace my nvidia 8600 gt. Once I put the new card in, my monitor does not even work. I know windows also does not start up because I do not hear the start up music. I had put my old card back in, worked just fine, but when I put the new one in, again blank screen. My fans, optic drive, and everything else seem to work. I do have an Optiquest Q7 monitor that does not have a dvi input, I had to use an adaptor, but the adaptor seem to work with my old video card. I'm really not sure what to do next, Thanks for your time.