Originally Posted by bobtomay

Here is a very good article I found about this issue on the Mac - an interesting read and very informative

After taking dtravis's suggestion and then reading that it could be an issue with the new drive itself -
Working on windows machines over the years - I would also check the following:
the molex connector is not plugged snugly enough into the drive - unplug and re-insert the connector making sure it is in all the way
the molex connector is faulty - try a different connector
power supply just not providing enough power - replace the PSU
newbie on the mac, so I do not know of a good application for checking voltages except a multi-meter