In no particular order, these are the top 12 things that slow your PC down:

Out Of Date Drivers

A Bloated Registry

Corrupted System Files

Corrupted Hard Disk

Out of Date Operating System Files

Viruses and Malware

Excessive Background Processes

Low Resources (Storage Space and CPU)

Out of Date Software

Overheating

Unoptimised Power Settings

Start-up Programs

Stick around to find out how to fix these problems, and if you get stuck, call me!