Thanks for the info osama_15.
It sounds like your CPU is throttling down due to excessive heat. If your rig is air cooled, then make sure that your cooling fans are working like they should and that your air filters are clean. If your rig is liquid cooled then ALSO make sure that your coolant pump is working and that any inline liquid filters are clean.
Use of canned air or even blowing through a drinking straw will help with cleaning out any dust or other blockages in your cooling fins/radiators.
If liquid cooled, also check to see if the fins located inside your cooling block may be clogged with debris (you have to take the block apart). This happens sometimes when/if the cooling solution breaks down or if the radiator(s) weren't rinsed out well before use.
Ensure that your CPU cooling fan or water block is seated snuggly. Sometimes vibration [over time] will loosen these up causing poor heat transfer from the CPU to your cooling system.
If your computer use to run great but started overheating, it is possible that the THERMAL PASTE between the CPU and cooling fan/water block may need to be reapplied. But check everything else first.
AGAIN, you need to run a 'monitor' program to see what your 'idle' and 'load' temperatures are. Without this information, everything is still a bit of a guess as to what the problem may be.
Montego13171