Hard drives won't boot

I'm trying to install a Hard drive into an old compaq presario who's HD failed. When I turn on the comp the Compaq logo appears on the screen and then it says Non-system disk or disk error. I know I have the Cables right. So I tried putting in this small spare HD I keep around and get a totally different error. this Time it says unable to access hard drive no operating system found. I know for a fact that both hard drives work.

 

Have you formatted the Hard Drives as they will need to be before the com will recognise them ..?? assuming of course that is the only (Master) HD in there.

 

Um No. and it is the only drive. It's been awhile since I've done this how do i format again.

 

If I take a hard drive out of an old comp that has an operating system on it still and put it in another comp do I still need to format it.

 

Yes,you will need your OS disk to format and install the new OS,if your adding the drive as a secondary you can format it in disk manager

 

Okay How do I do this.

 

http://forums.majorgeeks.com/showthread.php?t=25831