if its not a new computer, then it may be dirty. Dust and ect. can hinder airflow and prevent cooling, which will cause it to run constantly. This happens more frequently on notebooks, but also happens to desktops.
You can try getting a thing of canned air, and spraying out all the heatsinks, fans, ect. on your computer to get rid of dust and improve airflow
Thank you very much,the vents were covered by papers and dirt.