Check the Thermal Specification for the CPU if it is still within the range of operation.
Get your CPU SL number and search in the link below.
If it is much over the range then, check the following:
Make sure that you have a PSU Atx Version 2.2 at least.
Make sure that the chassis is TAC - Thermally Advantage Chassis
Check for proper aeration in the chassis. (cable)
Re-integrate the cpu with new small amount of thermal paste (clean the cpu before)
Check from the Board Manufacturer whether there is any bios update that addressed the thermal issues.
Try to test the system out of the chassis and see if it makes any difference.
Read the temperature directly in the BIOS.
If it is an Intel Board, use the Intel Desktop Utilities to monitor the temperature.
Other than this, i dont have any more suggestions.
All the best,