Black screen when turning on. Cause?

I want to make this clear, I have worked on ps2s for several years so it isn't the case the AV cord is bad or there is a cold solder joint on the AV port.

I have around 4 ps2s on hand that will turn on, appear to read disks and operate correctly, but the system never boots it's bios. This has nothing to do with the laser as I know even with out a laser it will still boot.

I am thinking it is a BGA issue, or something related to the BIOS chip. Has ANYONE seen this issue and was able to fix it? I do have a solder rework station and am very good with soldering as a foot note. System is NOT modded in anyway and appears I am the first person to open it. For reference, the issue is on mutable versions of the slim ps2 from v12 to the latest.

Any input please? As I said, I think it might be related to the BGAs on some chips, but would like other people's point of view. I will be reflowing one of the ps2s to attempt to see if this will make it boot.