So, I learned the hard way that the PS3 and 1.5TB internal drives are not 100% compatible.
I thought there was something wrong with the 1.5TB hard drive, so I returned it and got another one.
The replacement also didn't work.
I did some research and found out that 1TB internal drives are compatible.
So I need to return the second 1.5TB drive and order a 1TB drive.
I feel like an idiot, but I'm getting free returns with Amazon, so i only wasted time and effort.
Live and learn! 