Actually I'm thinking it could be the power supply. I read that the 5150 was never meant to have a hard drive (that's why the XT was made) so you needed to use a 5161 expansion system to add one. You also need the third revision of the BIOS (10/27/82).
This page has more info: http://www.minuszerodegrees.net/5150/problems/5150_known_problems_issues.htm
Today, 11:12 AM