1. CCleaner: This versatile tool can be used to clean up junk files, repair registry issues and optimize your PC.
2. Malwarebytes: This popular malware scanner can detect and fix issues that are causing your PC to slow down.
3. System Restore: The built-in Windows tool helps you restore important system files and settings that may have gone wrong.
4. Spybot Search & Destroy: This free tool can detect and remove spyware and other malicious programs that might be slowing your PC.
5. Disk Cleanup: Another Windows tool, Disk Cleanup can help you delete temporary files and free up disk space that is being used by unnecessary files.