In a gaming computer, overclocking is the process of tuning the components of the system to increase the clock speeds of the processing unit (CPU) and the graphics processing unit (GPU) to higher values. While overclocking is used more frequently in a CPU, an overclocked GPU is also considered overclocking, and the reason for this is the greater thermal limits the CPU and GPU allow. While any system that utilizes overclocking would not be classed as a "true" "gaming PC", overclocking still increases performance (as the CPU is clocked higher than it would be otherwise) and can be a handy way of increasing performance in the long term.
The major downside of overclocking is overheating. While it may sound simple, this is far from the case. Overclocking is a complex process, and the components of the system must work together to be able to achieve higher speeds. If anything is overheating, it will cause the system to stall, causing a loss of performance. As most people have tried overclocking, overheating is not the only problem but certainly one of the more common issues encountered when overclocking. If you want to overclock, you need to ensure your components have the appropriate voltages. The reason for this is to ensure components can run in the range that they were designed for. If the voltages are too low or too high, the components can fail and if there is a lack of a sufficient voltage supply, the system will stall (or become unstable).
Another common issue that arises when overclocking is the voltage supply. Typically, the power supply should be tested before use, to ensure it can provide the appropriate power. The problem with most power supplies is that they have fixed voltages which cannot be adjusted to match the needs of the system. This is usually caused by the motherboard requiring different power outputs for its different voltage regulators. Motherboards and video cards require different voltages and thus power requirements, and so for a power supply to be able to supply all the voltages required by the motherboard, it needs to be able to supply a lower voltage to the motherboard's voltage regulators (for the GPU and CPU). If the power supply is not able to do this, the voltage from the power supply will be reduced to the lowest amount of voltage, and thus not enough voltage will be supplied to both the GPU and the CPU.
The other problem that can occur when overclocking is that the system/BIOS might become unstable. This means the motherboard has stopped delivering a stable voltage to the voltage regulator. This causes the stalling and generally a loss of power. This issue can also occur due to several different problems such as power switch failure (due to an electrical fault caused by an unstable system) which can limit the output voltage supplied to the motherboard, causing a lack of power in the motherboard's voltage regulator.
Measures
1. The problems listed in the section are majorly due to overheating. To avoid such issues, make sure to install a proper cooling system on your PC.
2. Also, test the power supply, either by the motherboard's power switch or manually. Check if the power supply is delivering enough power to the motherboard for all the connections to components.