Greetings, This post might get lengthy as I want to be thorough in my explanation so I can get a proper diagnosis. I recently bought a Mac pro 2008 3,1 (2x 2.8 GHz quad-core, 8gb ram, ati 2600xt) and it ran fine when I first booted it up (running osx 10.8 at the time). Although the computer was working, the previous owner let a lot of dust accumulate inside. I installed Yosemite on the machine then shut it off. After that, I took the computer apart for dusting. I dusted each part with an air compressor then I reapplied heat sink paste to the CPUs. After reassembly, I press the power button and the GPU fan starts spinning at full speed. There is no chime and the computer doesn't boot. I removed the graphics card and power on again. The front light doesn't blink, so the computer isn't recognizing that there is a problem. Next, I removed the ram, same thing, no blinking front light. I tried resetting the smc, checking the diagnostic LEDs (http://imgur.com/B55Jhlg) but nothing seems to work. I did as much research as I could and concluded that it's a logic board issue. I thought I'd ask here first before buying one though. So TL;DR Bought a working but dusty Mac pro, dusted it, and now it doesn't work and am wondering if I should buy a new logic board or not.