Could be as simple as the ambient temp in your room where the computer is has risen. With the advent of winter some households will run the heat from time to time til it gets really cold then all the time.
If the case fans are sucking in warm or hot air then the cpu and other heat producing devices are hard pressed to get rid of the heat. If this is the case then you may want to conside setting up under a window in the room the computer is. It's naturally colder by a window in the fall and winter.
But then if this is not the case you also may want to consider reinstalling the heatsink and testing the cpu fan. Make sure you clean both the cpu chip and heatsink surfaces first before applying any thermal paste. And the paste of choice is Artic Silver 5.