The power system in those things can be tricky. Some GLODs are caused by bad PRAM batteries, as you have noticed, and those are curable. Unfortunately, when the power boards die, they also present the GLOD, and usually the COD (click of death) is also noticed. One of mine has a dead power board. It would boot sporadically when it felt like it, and then it quit booting altogether, the only signs of life being the click (a small pop sound from the speaker) and the green light. Swapping in a test power board from a working model restored its functionality. Putting the other power board in the other machine resulted in the same dead state, so I know where the problem lies, anyway.

I have yet to find a schematic for proper troubleshooting of these boards, and no individual components themselves test bad. I notice some odd voltage readings on my dead board, like there's a short somewhere, but haven't been able to isolate it. I dunno. A new power board is one thing I'll be looking into, when one turns up on eBay.

Fortunately, my other 2400s work properly for now (knock on wood).