Acer aspire 1670 problems

Question

it used to cut off which i realised it was overheating so i cleaned the cooling fans and it worked. then months later it cut off again i checked the fan i noticed one was only turning every now and then which made it overheat. i swapped the fans around to see if the fault would move across and it seemed ok. i put it all back together and it does not work at all. you press the power button and it goes on and off in seconds, sorry to go on but please help me