The build-up of dust can (and surely does) impact your computer's performance in two main ways: it causes the components of your computer to retain heat and makes it more difficult for the internal fans to dissipate heat from the system, thereby decreasing the efficiency of the entire system.

Can a dirty computer run slower?

Not really, the only way it will slow your computer down is that the fans get clogged or in general the airflow gets restricted, and the components start running hotter and because they get too hot the machine throttles down the clock on the GPU and/or the CPU.

Does cleaning PC make it faster?

However, everything degrades over time, and keeping your PC clean can help lengthen the life of such hardware and in return, yes, speed things up. ... PCs like to run cool, so the more airflow and cooler temperature you can achieve within the case, the better it will run.