Help to replace Graphics Card....Prior DIED!

My HIS AMD 6870 died. No video, no keyboard, no lights on USB units, and nothing. Substitute a older video card and keyboard lights lite, mouse connection lite, some USB units lite, no monitor lighting at all.

Pulled video card and replaced it with a ZOTAC GeForce GTX 550 Ti.

Obviously, could not remove the old video info and could not install the new. Computer now has the replacement card, keyboard lite, mouse lite, some USB lite, and no monitor lite. Currently set monitor to HDMI and graphics card to HDMI also.

How to I get this to light up the monitor so I can get the use of the computer again?

Need your help and instructions as to how to proceed.

Win7 SP1 64bit

HELP!!!!!!!!!!!!!!!!!

Changed monitors and up it came in the generic vga, deleted prior software, and installed the current software for the other card.

If I read this correctly, you've tried three cards and you get no monitor lighting.
It's possible that a backlighting element within the monitor may have failed.
You can try the monitor out on another computer to be sure.