Today I cleaned my entire rig for the 3rd time. I replaced thermal compound on my GPU, Southbridge, Northbridge and CPU and cleaned all dust. I put back everything and turned on POST ok and Windows loaded. All temps were excellent. After sometime, the system hanged. I rebooted it and POST always fails - no display. I removed gfx card(to boot from onboard VGA), usb 3 card and cleared CMOS. I removed both RAMs, no beeps from motherboard speaker, tried both sticks one at a time on all 4 slots. Nothing. Tried a different PSU- No luck. I am on the conclusion that the motherboard or CPU is dead. But the latter being uncommon, I suspect the mobo. Anyone who can shed some light on this? This is the very first time my computer is causing trouble.