new hard drive problems

I have a mac mini 2010 model that wouldnt boot . Technician looked at it and said most likely the hard drive. i purchased new drive and installed but when trying to instal os x leopard disk it won't recognize new drive therefore no disc utility. I plugged in a external usb drive and it recognized that. am I doing something wrong? needing some help!

Could it be the ribbon connection cable that's broken

I thought same thing but after taking apart again everything looked ok. I thought maybe i just couldnt see disk utility in bar above because of having using my 46 inch tv as a monitor. I swapped to a regular computer monitor . Still no disc utility! after rebooting for the third time and holding C key it finally showed. Figure that. New 500 gb drive now havin os installed.