thermal trip error (processor)shutdown pc

i was surfing net and pc closed i tried start it again and bip sound then it opened after a while and it showed thermal trip error processor: and now i started it again cpu dont seem that hot ill try change cpu fun i got pc 3 years
mobo is like 100 temp celcius and yes i know its bad but cant do anything with that if ichange mobo then ill have to buy new pc

anyway the error was from processor
and no dust
and yes everything is in its place
and yes i opened it
and yes i checked bios and hwmonitor in other post in this site and u told me something not right but cant do anything rater buy new pc or processor or mobo
i ll change processor fun