make sure there isnt dust clogging up the heatsink! mine got totally clogged and cpu temp went up to 75!!!!!! cleaned it, put 2 more case fans on, an inny and an outy spent about £20 on the pair, temps now well down
if you take the heatsink off the cpu you will need to buy some thermal conductor cleaner and some more thermal paste stuff to tansfer the heat from the cpu to the heatsink. if you dont put any on then you will be seeing that warning quite often!