just aim the space heater in the case… get it hot for 10 min and see if it turns on. it will be fine. its not a big deal and will tell you right away… i tried that with 3 machines, 2 were this common issue of BGA memory controller, the other was simple, pulled the video card out , popped it back in
and it was working flawlessly, right now i have a 2.7 ghz DP, liquid cooled,(hangin out under my desk) i tell you that once i have just one issue, i'm gutting the case,,, but so far its been rock solid, and i clean my my machines out every 6 months with 60 psi,(blow wand) a real air compressor in the garage,
i would like to guess that dust bunnies build up under the motherboard causing extra heat to build up, i'm sure the ROHS lead free solder does not help, however its easy to blame the solder, if you have your ventilation and your heat dissipation devices are working properly there is not going to be excess expansion , because the heat will be dispersed properly. unless there is a intensional design that ensures repeat business after a certain length of time.
witch i do not rule out! evil bastards lol.