I had a problem with my PC turning off which occurred in Ubuntu and Windows. I turned to the bios hardware monitor and found that heat was building up to 78+ degrees and then turning off. The case was full of fluff and dust which I cleared out. The (stock) fan/cooler was loaded with the stuff. No wonder it was overheating. Now I cleaned off the old thermal grease with isopropol alcohol, qtips, and a glasses cleaning cloth. I reapply a small amount of thermal grease. I had a lot of trouble with one push pin on the cooler but got that running. Each time I fit the cooler/fan I use fresh grease after cleaning off the old gunk. I found that the grease seems to be about right as, applying it in a small blob in the middle of the CPU, I found it covered the whole area of the cooler when I later took off the cooler (as cooling isn't working). The grease isn't leaking outside of the area of the heatsink so I guess my loading isn't excessive. The grease is Arctic silver 5. It may be a couple of years old. Is that the problem? The temperature still climbs up to about 80 before shutting off. I turn it off early now, once I see the cooling isn't working. Taking the other side of the case off, I can see that all four push pins are correctly seated on the motherboard. I check the CPU fan and it is working OK. The other case fans are working, but even they being off couldn't account for overheating like this. Any ideas?