What are some effective strategies for troubleshooting computer performance and stability issues?

If you have a custom build PC, especially if it's a gaming rig, you want to ensure that your components are being well cooled. Make sure the CPU fan is properly sized, reapply thermal paste as overheating will denature it and make it ineffective, and validate that you PSU is properly sized. Ideally you would draw no more than 50 - 60% under full load as it's most efficient in this range and will put out the least heat. Go with the most efficient PSU you can afford as it will put out less heat, cause a lower energy bill, and is better for the planet. If you are overclocking make sure to run burn in tests to confirm that your system is stable. Bad or poorly written code will crash an unstably overclocked PC.

You should clean your PC annually at a minimum, more often if you house is a dust trap or you have pets or small children. Make sure your setup is well positioned for optimal airflow; placing it backed up against a wall will reduce stability and shorten the lifespan of components. If your system has overheated before, replace the thermal paste as heat will cause it to denature and make the system worse off than if you just had metal on metal. Make sure your cables are all in good condition and not hyperextended or you can damage ports. Make sure to hit the power button after you unplug your system to fully discharge all capacitors prior to opening the case, and discharge any static charge that may be in play (clothes and PC/peripherals)

Make sure you take a holistic view of your system when upgrading. Are the motherboard or CPU going to be a bottleneck for your fancy new graphics card? Are you allocating enough RAM for your planned workload? Is your power supply sufficient to power your new components? Will thermal dissipation become an issue if your rig is tightly packed or you have a micro case? Make sure you take the time to thoroughly dust out your system when taking it apart for upgrade and plan to reapply thermal paste. It's also a good opportunity to rethink cable management even if your current setup is not a spaghetti mess. Modular power supplies can really clean up a system and improve performance by optimizing airflow. A cooler system is a more stable system.

Make sure that your OS is patched and antivirus definitions are up to date. Certain apps will run better when they are excluded from the AV processes, but make sure you are running legit versions of the program if you are going to make an exclusion as pirated apps can be loaded with malware (make sure you trust the vendor). Keep drivers up to date but test before and after, especially with graphics drivers, as new releases can have bugs that cause issues with HDMI, Displayport, Audio, artifacting, or overall performance so you want to be prepared to roll back to a stable version if you encounter issues. If you overclock look into undervolt strategies for your specific CPU and GPU as it will extend the hardware lifespan if done right.