Thing with computers errors and asking for advice, you really gotta say what the *exact* error message was. Interpetations always leads to wrong advice.
..also, I need to know, what kinda computer.. I ass-u-me a PC.
How many drives.. is it SCSI, IDE?
for now, best thing you can do (if you have a motherboard capable of HD autodetect) is plug in the sole hard drive alone, turn on the computer and see if
1. The hard drive starts to spin - feel it, listen to it.. dont open it

that means power is getting to it.
2. is it making any weird noises as it starts up? I should be fairly quiet
3. Is it being detected at boot up on your bios screen? yes? great.. no? try on a different channel.. (primary/secondary).. try different settings (master/slave - for scsi , ID 0 to 7).. Try a new cable.
if it doesnt detect... check on the drive, see how old it is, if its 3 years or younger... call the manufacture up and tell em your gonna claim your 3 year warranty
if it does, chances are it works, reformat it or something and try it again...
Hope this helps.