Anyone, please help me!
ALL transcoding software will work at 100% cpu. This is not a fault of the software, it will use as much CPU power as it can to get the job done in the quickest time. The priority setting is used to tell windows which tasks to perform first so if nothing else needs the CPU it will allow the transcoding program to use it.
It looks like your system does not have enough air flow inside the case to allow proper cooling of the CPU under high loads, I would suggest increasing the number of fans inside your case.