Open task manager, click on Details and click on the CPU to sort it by the load, see if you have any software that loads your CPU all the time.
Before you do that, add a GPU column too to see your GPU load per program.
Right click on the word Name or PID or Status or any of the words in the select bar, select option: Select Columns, it will pop up a new windows, scroll down and select GPU.
Now for ease of use, move the GPU column near the CPU one and start clicking on CPU, see your load and then on GPU and see its load.
If you have any programs that keep your CPU or GPU busy, they wiull show up there.