If it needs a new fan, definitely replace it >> If it needs replaced, sounds like it does?
While you have the box open, ensure you also get a can of compressed air and clear dust out
Don't let the fans spin from the force of the compressed air, hold them still with a Qtip
Careful inside the inside of the box, watch what you touch, touch a bare metal part of the chassis before getting your hands inside
Edit, are your drivers updated
Are you clear of spyware and malware?