1999 Cadillac EL Dorado steering problem

I was turning around and turning my wheel to the right and all of a sudden it felt like something let go and the car started making rumbling vibration sounds. If the wheels were straight, I didn't have any problem but turning either to the right or left, even slightly it made the same noise. I drove it htree miles to home and my husband checked the power steering fluid and it was full. I have the Northstar engine in this thing. My husband thinks it is the power steering pump and we are looking for some directions to change this on our own? What do you think? Do you know wher I could get step by step instructions? Do you think that is the problem? Please advise. Thank You.