I saw the same problem with a guy's v5 PS2 (which should be a GH-015 mobo), he had a Magic 3.1, the PS2 only boots CD-Rs, no DVD original/backup/movie, basically no DVD anything. He brought his console back to the place that modded it and they said that it was his laser. I wanted to try swapping his laser with a known working one but I didn't have any so I was not able to test it.
Many people here told me that it was a laser issue. But now I'm not so sure, check my thread here.
PS2 v5 NTSC U/C SCPH-30001R GH-015 w/Matrix Infinity