Cpu overheat and shutdown

hi.
i have a dual core athlon x2 4800+ @ 2,5 GHz on a Gigabyte GA-M61PME-S2 motherboardmn, 4 Gb RAM and ati 2400 hd gpu. problem is cpu overheats like crazy. while i'm writing this post the temperature is 30C (readings from everest). but if i'd go in a game, or install something, or do anything that uses a moderate amount of the CPU it will go in seconds to 60-70 and start to rise until hits 100-110 and goes into shutdown.
it's not the paste.. dust .. heatsink.. or whatever .. i've heard this 100 times .. cleaned . changed paste .. etc.
any solution? thanks