Hello, either your BIOS settings for your HDD are incorrect or you are missing the drivers for your motherboard.
Lets start with drivers first, you need to either find a resource CD that came with your computer and find the drivers on it. Copy them to flash drive and load the drivers from the flash drive during the win7 installation
if you don't have a CD you will have to go to manufacturer support website and look for drivers for your computer there, download them on a flash drive and load them during installation
Another problem you might be having is that you are trying to install windows on an existing file system that it does not recognize or it wasn't created using windows 7 tools. In such case I would advise to load using the old OS and back up all data from the hard drive, then get rid of any partitions that you have on it after that try installing windows 7.