After working without problems for a couple of years, your computer has begun to lock up. You suspect that it is a thermal issue but you can't find any component that is not functioning correctly. You have not replaced the CPU or installed any new devices. The CPU cooling fan and the power supply fan are working properly. The lock-ups are happening with increasing frequency.

Which of the following is a common condition that might explain these symptoms?

A. An accumulation of dust has gradually built up
B. The power supply has been switched to the wrong voltage setting
C. The BIOS has never been flashed and has gotten more and more out of date
D. The internal temperature sensor is beginning to malfunction intermittently