MacBook Pro, 15" Late 2008, 10.6.7 Model 2,2 2.16 ghz Core 2 Duo

Question

MacBook Pro, 15" Late 2008, 10.6.7 Model 2,2 2.16 ghz Core 2 Duo
This condition just sprang up.  Machine not dropped, no new parts added, OS stable, no single or significant change to anything on the box. No new external hardware. 
Did a restart and the following thing happens:
When power is initially put to the box, the screen lights up, and it displays a full screen, small checkerboard pattern.  You can see the Apple icon underneath the checkerboard.  The boot circle spins, and then the screen displays grey, and never makes it to blue.
So I tried to boot up in safe mode.  The same thing happens at the start of the boot sequence, however, after entering the safe mode, the startup proceeds normally, boots to the harddrive, and when the box changes from grey screen to blue screen, the checkerboard on the screen goes away and I have a perfectly good display, with everything working normally (but in the safe mode).
I have tried the following:
Boot from Apple CD . . . Still get the checkerboard pattern through grey screen, then as the OS loads, the pattern gets worse, (goes from a full screen pattern, to something like a "two page pattern" and it never gets to blue screen, you can never see the OS desktop.
Won't boot from USB drive.
Won't boot from external Dvd drive (Reads the disk, but won't boot, just like the internal drive).
Already changed RAM, RAM slots, etc.  Nothing plugged into any port.  Everything disconnected. 
Changed internal harddrives, same thing happens.  Zapped the PRAM, Firmware is good, etc.
Since this event happens no matter the harddrive, and the box won't startup from the Apple CD, I'm guessing it's a piece of hardware that has gone bad.
The only thing I can think to do, is to unplug all the different ancillary items, (ethernet, USB, airport, CD, etc), one at a time, off of the motherboard, and keep trying to start up normally in an effort to isolate the hardware that is bad.  In other words, if I unplug the airport card from the motherboard, and the machine starts normally, then I think I would have isolated the problem.  IF it does not start normally, unplug the next sub system, and try it again.
YEs, I did run Techtool Pro, and etc., and all systems passed.
Any thoughts ?
Thanks So much,
erebus
Doesn't the safe mode disable all the hardware sub-systems?  IS this why my machine starts in Safe, but won't boot normally ???

Answer 1

Yes, I boot up from the OS 10.6.3 installation disc and use Disc Utility to repair Disk and Permissions. I must tell you though, I've done the disc repair and permission repair quite a few times and it has never helped. Right now I've forgotten the OS disc in Luxemburg so I can only get it when I'm back in 3 weeks.
I ran Disc Utility today though and repaired permissions. The only one that wasn't fixed was an SUID-file.
I also checked the disc and it has some problems but I can't fix them until I get my OS disc or if I ask them to do it at the Genius Bar.
Yes, I have a Time Machine backup on an external usb HDD, last time I backed up was yesterday.