If a server is still overheating after cleaning dust from the fans, what is the BEST explanation for the problem?

When a server continues to overheat despite cleaning dust from the fans, a likely root cause is that some of the cooling fans are defective. Fans play a critical role in maintaining optimal airflow and dissipating heat generated by the server's components. If one or more fans are not functioning properly—whether they are failing to spin at the required RPM or are completely inoperative—the airflow will be insufficient to cool the internal hardware effectively, leading to elevated temperatures.

In contrast, a failed power supply would typically show symptoms unrelated to overheating, such as server instability or failure to power on. Excessive power usage may contribute to a heating problem but usually wouldn't occur in isolation; a correctly-functioning system has built-in protections. Lastly, while hard drives can generate heat, they are usually not the primary concern compared to the cooling system's effectiveness in maintaining overall system temperatures. The failure of fans would directly compromise the server’s cooling system and is therefore a vital factor in diagnosing persistent overheating issues.