Powermac G5 won't boot - but safe mode works fine!!!

[The computer described below is a Powermac G5 dual core 2.7gHz, purchased in late 2005, running OS X 10.4.11]

Here's an odd thing... a few months back, my powermac stopped booting. It wasn't a power supply issue. I would get the white screen with the apple to come up, but when it was time for the blue screen with the user logins, the screen would go black.

I tried swapping out all the RAM, and nothing worked. Was able to get safe mode to work, once, and then never again. Finally I broke down and took my baby to Tekserve.

Tekserve took a MONTH to get it back to me, and they claimed it was a bad RAM set. This sounded really odd to me, since I thought I had correctly tested several sticks of RAM, and even no RAM, without any success. But I'm not one of the experts, so, hey. My computer was running again and that's all I cared about.

Well, now, about 3 weeks later, my computer will not boot. It started with the loud fans. Now I'm not having any fan noise, but it still won't boot. Here's how I've troubleshot it so far:

- The computer boots FINE in safe mode. I verified the disc in safe mode, and everything checks out. Everything also checks out using fsdk -fy in single user mode. So no disc problem, apparently.

- When I reset the PRAM using crtl opt+pr after the chime, the screen resolution changes from 1200x1024 to 800x600. After the white screen, I do get the blue screen, but WITHOUT any user login, and the mouse cursor does not show up.

- When I reset the NVRAM using open firmware (reset-nvram, set-defaults, reset-all), I'm back to my normal problem of white screen followed by black nothingness (and emotional despair).

Tonight I'm going to try swapping out the RAM again, but if that doesn't work, what's next? I don't know where I put the original Hardware Test DVD that came with the powermac... is there a program I can buy to see if this is my logic board, without bringing the powermac back into tekserve? I live in NYC and have no car; bringing this heavy item into Manhattan is a real issue for me!!!

Anyways, any and all info is greatly appreciated. I really hope I'm overlooking something obvious. Natch, neither Apple nor Tekserve want to give me any advice without me shelling over more of my hard-earned cash. And this all went down 3 months after applecare expired... sigh...