There can be a number of reasons why the drive is not detected.
1. The drive formatted as one large partition is not compatible with the system.
2. The drive is not jumpered correctly to be compatible with the system.
3. The hard drive is too large for the system's bios to recognize it.
What is the make and model of the system, as well as the hard drive?
You may have to partition the drive using the hard drive manufacturer's utility (on the system that you expect to use it on) for the utility to format it properly, then for the system detect it properly.
_________________________
"I love it when a plan comes together." - Hannibal Smith