Compaq Armada 7800 Hard Driver Failure HELP ME!!!?

When I turn on my Compaq Armada 7800, It says Disk Controller Failure. So the Hard Drive is DEAD. I got a new hard drive (Still keeping old one) and when plugged in, it says ***Non System Disk or Disk Failure. Replace and Strike any key*** What do I do? Im not good with tech stuff!!! PLEASE make this easy for me!