This is why I always test the components outside the case before fitting inside the case.
Saved me a lot of hassle the other day upgrading my daughter's PC as it turned out the supplied thermal paste with the cooler was terrible, and was causing 95 degree temps under stress test.
Removed the cooler, cleaned and repasted the CPU with Thermal Grizzly and refitted the cooler and now it's 82 degrees max, which is ok for a cheap air cooler.
Darn sight easier removing, repasting and refitting a cooler outside the case!
I also ran a memtest before fitting the MB.
Saves so much hassle to check for failed components before starting the build proper.