From the website below:
The maximum threshold temperature is 74.1 C, but some it can go above the value +5C, it is still ok.
When the cpu overheats, on some boards, you will get an alarm (siren), there is no error message, possibly in the event log in the bios, it may mention something on the cpu temperature.
It all depends on which board you have, as in new desktop board, in the bios there is a new parameter, which is called ProcHot.
Advanced >> Hardware Configuration
a) ProcHot must be negative.
For example, if the temperature is -21C, this means that it is still ok, as you have 21 more degrees to go for it to be critical.
b) Use the tools from Intel to read the temperature for Intel Desktop Board
temperature at which the CPU will start throttling itself in order to remain cool enough. Throttling means skipping clock cycles.
Hope this helps a bit.