STOP - look carefully at the grease patch on your new CPU - was it protected by a plastic cover? when you unccover it, is it soft and easily marked with a fingertip? was it a thin, even coating over most of the bottom of the heatsink?
If so, that is a NEW swab of thermal grease put there already for you - relax and just fit it.
You only need to remove OLD thermal paste that has been cooked, ...



