Can a virus cause my PC to slow down? By YL ComputingSpeed Up PC Yes, a virus can cause your PC to slow down. Viruses can slow down your computer by taking up system resources and running processes in the background, which can make your computer appear to be running more slowly than usual. Related Content:Are there any good software tools available to optimize my PC performance?What software should I use to improve my PC's performance?How do I optimize my system for better performance?