Which issue is most likely causing a computer to overheat?

Overheating in a computer typically results from inadequate cooling systems, which can include issues such as malfunctioning fans, clogged air vents, or dried-up thermal paste. The cooling system is designed to dissipate heat generated by the CPU, GPU, and other components. When there is a failure in any part of this cooling mechanism, the heat cannot be effectively managed, leading to increased temperatures inside the case. This situation can cause thermal throttling, system instability, or even permanent damage to hardware components.

The other options do not directly relate to overheating in a clear and immediate manner. While power supply failure can lead to various system issues, it is less likely to directly cause overheating. Insufficient RAM can result in performance slowdowns but does not produce heat in the same manner. Similarly, disk fragmentation affects data retrieval times and drive performance but is not associated with increased heat generation in computer components.