Sounds to me like: 1: dust in your PC (here in Germany we call it "Wollmäuse" --- "wool mice" Some Towers / fans have dust filters, check them too
2; One ore more fans is/are not working properly
3: your fans are not able to transport the heat outside your tower. Check this. If you have checked 1 & 2 and you can confirm that everything seems to be OK, I would suggest that you post some pictures of your tower: Front, back, top and sides. The best pictures are from inside, so that we all can see all your fans. You can also open your tower, start to play and observe the temperatures. But be careful: this changes the airflow within your tower and can(!) make the situation worse. But mostly it helps to get rid of the hot air in the tower But this shouldn't be a permanent solution!