dead logic board?

I've got a 2008 Aluminum (unibody) MacBook. Used it this morning with no problems, then shut the lid and brought it to work. When I pulled it out a few hours later, the entire thing was pretty hot (not scorching, but way hotter than a sleeping computer should be) and I noticed from the battery indicator that the battery had been run down a good 40% or so (from 100% that morning). The computer was apparently frozen and stuck at a grey screen when I opened it up.

After a force reboot, it won't get past the grey screen -- power turns on, cd drive whirrs, then it hangs at the grey screen indefinitely with no further signs of life. Everything I have tried has been to no effect:

• Reboot (many times), with and without power connected, including physically disconnecting the battery
• Boot into safe mode
• Boot with option key to try to get to the boot disk selector
• Reset NVRAM/PRAM
• Checking for bad RAM by booting with just one, then just the other stick

Every reboot is just power, cd whirr, grey screen, hang. At this point I'm guessing the logic board is toast and the computer is pretty much hosed, which sucks because I'd say it's on the border between where replacing the logic board vs the entire machine makes sense.

But just on the offchance I'm missing something, anyone have any other ideas as to what the problem could be?

 

I can't even get to the boot selection screen -- holding option does nothing, so it's not a dead hard drive (otherwise I'd expect to get to the selection screen with no options).