Dirt, dust, and hair can accumulate very easily on and in your PC tower. A dirty PC can cause overheating issues and damage the motherboard and other internal components. Every few months you should physically clean your PC. Always have on hand a can or two of compressed air designed for electronic cleaning.
Before cleaning, shut down the PC, unplug all the cables, and move the PC to a clean table. Then remove the side panel(s) from the PC. If you find a significant mess, it might be better to clean it in the garage.
Use a can of compressed air to blow out the dirt, dust, and hair inside the PC. Position the PC so you can blow out the mess rather than just blow it around the insides. You can carefully pull out clumps. But never use a vacuum during cleaning as it can create static electricity and damage the components.
Remember to create a System Restore point before you start cleaning. You can use tools (such as Glary Utilities) to help you clean and optimize Windows. Ensure you have a current anti-virus utility installed and double-check for infections with another scanner (such as Malwarebytes) as well. You can free up disk space by deleting or archiving old files and documents. Finish up the software-based cleaning by running Disk Defragmenter and Check Disk on your drive(s).
When physically cleaning, remember to keep yourself grounded to the metal frame of the PC, and always keep the can of compressed air upright.
Now check out your computer; you might notice it runs smoother. Remember to repeat the process every few months.