Overheating in tosh sat pro 4600

Question

hi..
if the fan is constantly on while i play an rpg the fps remains a stable average 25... is there a way  i can turn the fan on manually because it doesnt' always turn on when i start the rpg ? ... is there a way i can fix the overheat prob. so i don't need constant fan cooling ? ... for 3 years it played perfectly until 2 weeks ago... i have created new partition and reinstalled xp pro and game there... same prob.. or can i get a new fan and install  it myself ?... is it easy for a computer dummy like me ? ... if so do you know what model fan i need to get for this puter ?