When a DC computer case fan malfunctions, there are several steps you can take to troubleshoot the problem. If the fan is not spinning at all, first check the power connection. Make sure that the fan's power cable is properly plugged into the motherboard or the fan controller. Sometimes, the cable may become loose over time, causing a loss of power.

If the power connection is fine, but the fan is still not working, it could be a problem with the fan's motor. You can try gently spinning the fan blades by hand. If the blades move freely and then stop, the motor may be faulty. In some cases, the motor may be seized due to a lack of lubrication or excessive dust accumulation. You can try applying a small amount of lightweight lubricant, such as sewing machine oil, to the bearings.

If the fan is spinning but making unusual noises, it could be due to unbalanced blades. Check if there is any debris stuck on the blades or if the blades are bent. Remove any debris and, if possible, straighten the bent blades carefully. If the noise persists, it may be a sign of bearing failure, and you may need to replace the fan.